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/docker-publish.yml

@@ -30,7 +30,7 @@ jobs:
 
             - name: Extract metadata (tags, labels) for Docker
               id: meta
-              uses: docker/metadata-action@v5
+              uses: docker/metadata-action@v6
               with:
                   images: |
                       opengeos/mapwidget