Skip Ractor test on mingw where Pathname::SAME_PATHS is not shareable

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

test/pathname/test_ractor.rb

@@ -8,6 +8,7 @@ def setup
   end
 
   def test_ractor_shareable
+    omit "Ractor with Pathname is not supported on mingw" if /mingw/ =~ RUBY_PLATFORM
     assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
     class Ractor
       alias value take