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](https://github.com/docker/metadata-action/compare/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>

.github/workflows/docker-alpine.yml

@@ -64,7 +64,7 @@ jobs:
       # Get Metadata for docker_build step below
       - name: Sync metadata (tags, labels) from GitHub to Docker for 'snipe-it' image
         id: meta_build
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: snipe/snipe-it
           tags: ${{ env.IMAGE_TAGS }}

.github/workflows/docker-ubuntu.yml

@@ -64,7 +64,7 @@ jobs:
       # Get Metadata for docker_build step below
       - name: Sync metadata (tags, labels) from GitHub to Docker for 'snipe-it' image
         id: meta_build
-        uses: docker/metadata-action@v5
+        uses: docker/metadata-action@v6
         with:
           images: snipe/snipe-it
           tags: ${{ env.IMAGE_TAGS }}