Bump docker/metadata-action from 5.5.1 to 5.6.1

Bumps [docker/metadata-action](https://github.com/docker/metadata-action) from 5.5.1 to 5.6.1.
- [Release notes](https://github.com/docker/metadata-action/releases)
- [Commits](docker/metadata-action@v5.5.1...v5.6.1)

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

Signed-off-by: dependabot[bot] <[email protected]>

.github/workflows/docker.yml

@@ -31,7 +31,7 @@ jobs:
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
-        uses: docker/metadata-action@v5.5.1
+        uses: docker/metadata-action@v5.6.1
         with:
           images: nipreps/fmripost-template
           # generate Docker tags based on the following events/attributes