Bump actions/checkout

Author: m-nakamura145

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/rails_${{ matrix.rails }}.gemfile
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1