Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/container-build.yaml

@@ -11,7 +11,7 @@ jobs:
       packages: write
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3