Update docker/metadata-action action to v6

Author: renovate[bot]

.github/workflows/docker.yml

@@ -22,7 +22,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: docker/setup-buildx-action@v3
       - id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: ghcr.io/${{ github.repository }}
           tags: |