Fix unit tests when default timezone is not UTC

[andsel]

Fixes ruby unit test in case the running host has a default timezone different than UTC, configuring the plugin to use UTC timezone.

Without specifying the timezone in the test, it brings the default from the system. The extraction of year from Logstash's Timestamp is done in UTC timezone:

final int year = this.timestamp.toInstant().atOffset(java.time.ZoneOffset.UTC).getYear();

Creating a timestamp in a timezone different from UTC generates the error:

Failures:

  1) LogStash::Filters::Date cancelled events cancelled events list ignores and return ignored cancelled
     Failure/Error: expect(result[2].timestamp.year).to eq(uncancelled_year)

       expected: 2001
            got: 2000

       (compared using ==)
     # ./spec/filters/date_spec.rb:871:in `block in <main>'
     # /usr/share/rvm/gems/jruby-9.2.9.0/gems/logstash-devutils-2.4.0-java/lib/logstash/devutils/rspec/spec_helper.rb:61:in `block in <main>'

Finished in 0.16188 seconds (files took 3.09 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./spec/filters/date_spec.rb:862 # LogStash::Filters::Date cancelled events cancelled events list ignores and return ignored cancelled

How to test

• setup an enviroment with

  export LOGSTASH_PATH= && export LOGSTASH_SOURCE=1

• check your default timezone differs from UTC
• run the test

  bundler exec rspec spec/filters/date_spec.rb:862

• on main must fail while in this branch success.