When rubygems_plugin.rb is not found, test_rdoc_rubygems_hook.rb is skipped.

Author: mterada1228

.github/workflows/ruby-core.yml

@@ -55,5 +55,5 @@ jobs:
           ruby tool/sync_default_gems.rb rdoc
         working-directory: ruby/ruby
       - name: Test RDoc
-        run: make -j2 -s test-all TESTS="rdoc --no-retry --exclude test_rdoc_rubygems_hook.rb"
+        run: make -j2 -s test-all TESTS="rdoc --no-retry"
         working-directory: ruby/ruby

test/rdoc/test_rdoc_rubygems_hook.rb

@@ -2,9 +2,13 @@
 require 'rubygems'
 require 'fileutils'
 require 'tmpdir'
-require_relative '../../lib/rubygems_plugin'
 require 'test/unit'
 
+begin
+  require_relative '../../lib/rubygems_plugin'
+rescue LoadError
+end
+  
 class TestRDocRubyGemsHook < Test::Unit::TestCase
   def setup
     @a = Gem::Specification.new do |s|
@@ -284,4 +288,4 @@ def test_setup_unwritable
     end
   end
 
-end
+end if defined?(RDoc::RubyGemsHook)