Upgrade workflows to actions/checkout@v3

Author: bdunne

.github/workflows/ci.yaml

@@ -31,7 +31,7 @@ jobs:
       PGPASSWORD: smartvm
       CC_TEST_REPORTER_ID: "${{ secrets.CC_TEST_REPORTER_ID }}"
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up system
       run: bin/before_install
     - name: Set up Ruby