fix deprecated syntax: Wrapping Vararg directly in UnionAll

[nsajko]

Syntax like this seems to be deprecated: inds::Vararg{<:Integer,N}, so I removed the <:.

$ julia -O3 --min-optlevel=3 --depwarn=error --warn-overwrite=yes
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.10.0-DEV.453 (2023-01-28)
 _/ |\__'_|_|_|\__'_|  |  Commit 7d4309c9c31 (0 days old master)
|__/                   |

julia> using OffsetArrays
[ Info: Precompiling OffsetArrays [6fe1bfb0-de20-5000-8ca7-80f57d26f881]
ERROR: LoadError: Wrapping `Vararg` directly in UnionAll is deprecated (wrap the tuple instead).
Stacktrace:
 [1] UnionAll(v::TypeVar, t::Any)
   @ Core ./boot.jl:257
 [2] top-level scope
   @ ~/tmp/OffsetArrays.jl/src/OffsetArrays.jl:660

Fixes #324

[codecov[bot]]

Codecov Report

Merging #325 (1b6ecf4) into master (08dc371) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #325   +/-   ##
=======================================
  Coverage   98.67%   98.67%           
=======================================
  Files           5        5           
  Lines         452      452           
=======================================
  Hits          446      446           
  Misses          6        6           

Impacted Files	Coverage Δ
src/OffsetArrays.jl	98.29% <100.00%> (ø)

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[jishnub]

Looks good! Could you bump the patch version? I'll merge and tag