[rubygems/rubygems] Disabled to test rustc with msys2 platform.

https://github.com/rubygems/rubygems/actions/runs/4598776839/jobs/8123290246

https://github.com/rubygems/rubygems/commit/5c3b0a112e

test/rubygems/helper.rb

@@ -1175,6 +1175,20 @@ Also, a list:
     RUBY_PLATFORM.match("mswin")
   end
 
+  ##
+  # Is this test being run on a version of Ruby built with mingw?
+
+  def self.mingw_windows?
+    RUBY_PLATFORM.match("mingw")
+  end
+
+  ##
+  # Is this test being run on a version of Ruby built with mingw?
+
+  def mingw_windows?
+    RUBY_PLATFORM.match("mingw")
+  end
+
   ##
   # Is this test being run on a ruby/ruby repository?
   #

test/rubygems/test_gem_ext_cargo_builder.rb

@@ -145,6 +145,7 @@ class TestGemExtCargoBuilder < Gem::TestCase
     system(@rust_envs, "cargo", "-V", out: IO::NULL, err: [:child, :out])
     pend "cargo not present" unless $?.success?
     pend "ruby.h is not provided by ruby repo" if ruby_repo?
+    pend "rust toolchain of mingw is broken" if mingw_windows?
   end
 
   def assert_ffi_handle(bundle, name)