Stochastic failure in thread-safety tests

Noticed this failure on "Julia 1.6 - windows-latest - x64". I'm not seeing the source of the failure so it seemed best to track this in an issue:
 Testing Running tests...
[ Info: Installing 2016j tzdata region data
[ Info: Downloading Windows to POSIX timezone ID XML version: release-40
[ Info: Compiling Windows time zone name translation
[ Info: Running Thread Safety tests
Multithreaded TimeZone construction: Error During Test at D:\a\TimeZones.jl\TimeZones.jl\test\thread-safety.jl:65
  Got exception outside of a @test
  failed process: Process(`'C:\hostedtoolcache\windows\julia\1.6.6\x64\bin\julia.exe'-Cnative'-JC:\hostedtoolcache\windows\julia\1.6.6\x64\lib\julia\sys.dll'--depwarn=yes--check-bounds=yes-g1--code-coverage=user--color=yes--startup-file=no--proj-E"using TimeZones
using Test
[ Info: Installing 2016j tzdata region data
[ Info: Converting tz source files into TimeZone data
@assert Threads.nthreads() > 1 \"This system does not support multiple threads, so the thread-safety tests cannot be run.\"
@testset \"Multithreaded TimeZone brute force test\" begin
    function create_zdt(year, month, day, tz_name)
        ZonedDateTime(DateTime(year, month, day), TimeZone(tz_name))
    end
    function cycle_zdts()
        return [
            try
                create_zdt(year, month, day, tz_name)
            catch e
                # Ignore ZonedDateTimes that aren't valid
                e isa Union{ArgumentError,AmbiguousTimeError,NonExistentTimeError} || rethrow()
                nothing
            end
            for year in 2000:2020
            for month in 1:5
            for day in 10:15
            for tz_name in timezone_names()
        ]
    end
    outputs = Channel(Inf)
    @sync begin
        for _ in 1:15
            Threads.@spawn begin
                put!(outputs, cycle_zdts())
            end
        end
    end
    close(outputs)
    tzs = collect(outputs)
    # Test that every Task produced the same result
    allsame(x) = all(y -> y == first(x), x)
    @test allsame(tzs)
end
#----------------------------------------------------
@testset \"Interleaved compile() and TimeZone construction\" begin
    @sync for i in 1:20
        if (i % 5 == 0)
            TimeZones.TZData.compile()
        end
        Threads.@spawn begin
            TimeZone(\"US/Eastern\", TimeZones.Class(:LEGACY))
        end
    end
end
"`, ProcessExited(3221225477)) [3221225477]
  Stacktrace:
    [1] pipeline_error
    @ .\process.jl:538 [inlined]
    [2] run(::Cmd; wait::Bool)
    @ Base.\process.jl:453
    [3] run
    @ .\process.jl:451 [inlined]
    [4] (::var"#173#174")()
    @ MainD:\a\TimeZones.jl\TimeZones.jl\test\thread-safety.jl:70
    [5] withenv(f::var"#173#174", keyvals::Pair{String, Int64})
    @ Base.\env.jl:161
    [6] macro expansion
    @ D:\a\TimeZones.jl\TimeZones.jl\test\thread-safety.jl:69 [inlined]
    [7] macro expansion
    @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
    [8] top-level scope
    @ D:\a\TimeZones.jl\TimeZones.jl\test\thread-safety.jl:67
    [9] include(fname::String)
    @ Base.MainInclude.\client.jl:444
   [10] macro expansion
    @ D:\a\TimeZones.jl\TimeZones.jl\test\runtests.jl:71 [inlined]
   [11] macro expansion
    @ C:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Test\src\Test.jl:1151 [inlined]
   [12] top-level scope
    @ D:\a\TimeZones.jl\TimeZones.jl\test\runtests.jl:38
   [13] include(fname::String)
    @ Base.MainInclude.\client.jl:444
   [14] top-level scope
    @ none:6
   [15] eval
    @ .\boot.jl:360 [inlined]
   [16] exec_options(opts::Base.JLOptions)
    @ Base.\client.jl:261
   [17] _start()
    @ Base.\client.jl:485
[ Info: Compiling Windows time zone name translation
[ Info: Successfully built TimeZones
Test Summary:                         | Pass  Error  Broken  Total
TimeZones                             | 1781      1       2   1784
  IndexableGenerator                  |    9      9
  Class                               |   30     30
  tzdata_versions                     |    2      2
  tzdata_latest_version               |    4      4
  tryparse_dayofmonth_function        |    7      7
  compile                             |   79     79
  istimezone                          |    3      3
  etcetera                            |    9      9
  FixedTimeZone                       |   36     36
  VariableTimeZone                    |   24     24
  ZonedDateTime                       |  210    210
  Exceptions                          |    3      3
  ParseNextError                      |    8      8
  lt_local / lt_utc                   |   12     12
  transition_range                    |   20     20
  StepRange{ZonedDateTime}            |   18     18
  Transitions I/O                     |    5      5
  read_signature                      |    2      2
  read_version                        |    5      5
  combine_designations                |    9      9
  write_signature                     |    1      1
  write_version                       |    5      5
  write                               |    3       2      5
  read_signature                      |    2      2
  read_version                        |    2      2
  read                                |    7      7
  write_signature                     |    1      1
  write_version                       |    3      3
  write                               |    6      6
  Construct ZonedDateTime / DateTime  |    4      4
  Construct Date / ZonedDateTime      |    4      4
  Construct Time                      |    3      3
  now                                 |    2      2
  today                               |    2      2
  todayat                             |    4      4
  System TZ behaviour                 |                      No tests
  localzone                           |   14     14
  legacy time zones                   |    5      5
  next_transition_instant             |   12     12
  show_next_transition                |   10     10
  parse                               |    5      5
  tryparse                            |    2      2
  parse components                    |    1      1
  default format                      |    1      1
  parse constructor                   |    6      6
  _parsesub_tzabbr                    |   12     12
  _parsesub_offset                    |   28     28
  _parsesub_time                      |    3      3
  _parsesub_tzdate                    |   56     56
  _parsesub_tz                        |   40     40
  ZonedDateTime plot recipe           |    9      9
  Multithreaded TimeZone construction |           1      1
  build process                       |   15     15
ERROR: LoadError: Some tests did not pass: 1781 passed, 0 failed, 1 errored, 2 broken.
in expression starting at D:\a\TimeZones.jl\TimeZones.jl\test\runtests.jl:37
ERROR: Package TimeZones errored during testing
Stacktrace:
 [1] pkgerror(msg::String)
   @ Pkg.TypesC:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Pkg\src\Types.jl:55
 [2] test(ctx::Pkg.Types.Context, pkgs::Vector{Pkg.Types.PackageSpec}; coverage::Bool, julia_args::Cmd, test_args::Cmd, test_fn::Nothing)
   @ Pkg.OperationsC:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Pkg\src\Operations.jl:1708
 [3] test(ctx::Pkg.Types.Context, pkgs::Vector{Pkg.Types.PackageSpec}; coverage::Bool, test_fn::Nothing, julia_args::Vector{String}, test_args::Cmd, kwargs::Base.Iterators.Pairs{Symbol, IOContext{Base.PipeEndpoint}, Tuple{Symbol}, NamedTuple{(:io,), Tuple{IOContext{Base.PipeEndpoint}}}})
   @ Pkg.APIC:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Pkg\src\API.jl:343
 [4] test(pkgs::Vector{Pkg.Types.PackageSpec}; io::IOContext{Base.PipeEndpoint}, kwargs::Base.Iterators.Pairs{Symbol, Any, Tuple{Symbol, Symbol}, NamedTuple{(:coverage, :julia_args), Tuple{Bool, Vector{String}}}})
   @ Pkg.APIC:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Pkg\src\API.jl:80
 [5] test(; name::Nothing, uuid::Nothing, version::Nothing, url::Nothing, rev::Nothing, path::Nothing, mode::Pkg.Types.PackageMode, subdir::Nothing, kwargs::Base.Iterators.Pairs{Symbol, Any, Tuple{Symbol, Symbol}, NamedTuple{(:coverage, :julia_args), Tuple{Bool, Vector{String}}}})
   @ Pkg.APIC:\buildbot\worker\package_win64\build\usr\share\julia\stdlib\v1.6\Pkg\src\API.jl:96
 [6] top-level scope
   @ none:1
Error: Process completed with exit code 1.
– https://github.com/JuliaTime/TimeZones.jl/runs/7252748476?check_suite_focus=true
JuliaTime / TimeZones.jl

Stochastic failure in thread-safety tests #386
