fix(deps): update actions/checkout action to v4

Author: Self-hosted Renovate Bot

.github/workflows/renovate_config_validator.yml

@@ -14,6 +14,6 @@ jobs:
   validate:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@3df4ab11eba7bda6032a0b82a6bb43b11571feac # v4
       - name: Validate the config
         uses: suzuki-shunsuke/github-action-renovate-config-validator@v0.1.2