Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/docker.yaml

@@ -16,7 +16,7 @@ jobs:
       id-token: write
     steps:
       - name: Check out the repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Log in to Docker Hub
         uses: docker/login-action@v3