Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/ci.yml

@@ -9,6 +9,6 @@ jobs:
   policy:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@ec3a7ce113134d7a93b817d10a8272cb61118579 # renovate: tag=v2.4.0
+      - uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4.2.1
       - uses: docker://ghcr.io/example-policy-org/policy-checker:latest