Update checkout action to resolve Node v12 deprecation warning

Author: petergoldstein

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
         ruby: [2.7, '3.0', 3.1, 3.2]
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true