Partly reverted ruby-core job for breaking repository url on stable branch

Author: hsbt

.github/workflows/ruby-core.yml

@@ -42,7 +42,7 @@ jobs:
         working-directory: ruby/ruby
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
-          path: ruby/rubygems
+          path: rubygems/rubygems # We need to backport repository url to sync_default_gems.rb of `ruby_3_4` branch.
           persist-credentials: false
       - name: Sync tools
         run: |