[rubygems/rubygems] Skip extension test on jruby

https://github.com/rubygems/rubygems/commit/38ee82c297

test/rubygems/test_gem_commands_exec_command.rb

@@ -216,6 +216,8 @@ class TestGemCommandsExecCommand < Gem::TestCase
   end
 
   def test_gem_with_platform_and_platform_dependencies
+    pend "extensions don't quite work on jruby" if Gem.java_platform?
+
     platforms = Gem.platforms.dup
 
     spec_fetcher do |fetcher|