Bump docker/metadata-action from 5 to 6

Bumps [docker/metadata-action](https://github.com/docker/metadata-action) from 5 to 6.
- [Release notes](https://github.com/docker/metadata-action/releases)
- [Commits](docker/metadata-action@v5...v6)

---
updated-dependencies:
- dependency-name: docker/metadata-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/build.yml

@@ -154,7 +154,7 @@ jobs:
       - name: Extract metadata
         if: steps.check.outputs.exists == 'false'
         id: meta
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: ghcr.io/${{ github.repository_owner }}/python-container-builder
           tags: |