Update actions/checkout to the latest version

The latest version of actions/checkout is v5 now.

ref: https://github.com/actions/checkout

Author: willnet

.github/workflows/ruby.yml

@@ -29,7 +29,7 @@ jobs:
       BUNDLE_GEMFILE: gemfiles/rails_${{ matrix.rails }}.gemfile
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v5
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: