Merge pull request #666 from amatsuda/checkout_v3

Fix build warnings in the CI by using actions/checkout@v3

.github/workflows/ruby.yml

@@ -61,7 +61,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with: