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@a12a3943b4bdde767164f792f33f40b04645d846 # tag=v3.0.0
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4.0.0
       - uses: docker://ghcr.io/example-policy-org/policy-checker:latest