Skip flaky test_with_webauthn_enabled_failure on TruffleRuby

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

Author: hsbt

test/rubygems/test_gem_commands_yank_command.rb

@@ -141,6 +141,7 @@ def test_with_webauthn_enabled_success
   end
 
   def test_with_webauthn_enabled_failure
+    pend "Flaky on TruffleRuby" if RUBY_ENGINE == "truffleruby"
     server = Gem::MockTCPServer.new
     error = Gem::WebauthnVerificationError.new("Something went wrong")