VLN-1481: remediate unpinned-github-actions (#23)

Author: picatz

.github/workflows/require-codeowners.yml

@@ -36,7 +36,7 @@ jobs:
 
     steps:
       - name: Checkout branch
-        uses: actions/checkout@v6
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
         with:
           ref: ${{ github.event.pull_request.head.sha }}