Omit assert_ractor with Windows platform

Author: hsbt

tool/lib/core_assertions.rb

@@ -391,6 +391,7 @@ def assert_separately(args, file = nil, line = nil, src, ignore_stderr: nil, **o
       # Run Ractor-related test without influencing the main test suite
       def assert_ractor(src, args: [], require: nil, require_relative: nil, file: nil, line: nil, ignore_stderr: nil, **opt)
         return unless defined?(Ractor)
+        omit if windows?
 
         # https://bugs.ruby-lang.org/issues/21262
         shim_value = "class Ractor; alias value take; end" unless Ractor.method_defined?(:value)