Revert check_react_and_ujs to Ruby 2.7

The lockfiles are compatible with Ruby 2.7 but not Ruby 3.3 (nokogiri
version conflicts). Revert to Ruby 2.7 to match main branch behavior.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: justin808

.github/workflows/ruby.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        ruby: ['3.3']
+        ruby: ['2.7']
     runs-on: ubuntu-latest
     env:
       PACKAGE_JSON_FALLBACK_MANAGER: yarn_classic