Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/validate.yml

@@ -17,7 +17,7 @@ jobs:
   verify-yaml:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Validate JSON
         uses: GrantBirki/[email protected]