Bump docker/build-push-action from 6.7.0 to 6.9.0

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 6.7.0 to 6.9.0.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v6.7.0...v6.9.0)

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

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

.github/workflows/release-publish.yml

@@ -42,7 +42,7 @@ jobs:
           username: flowfuse
           password: ${{ secrets.DOCKER_HUB_PASSWORD }}
       - name: Build and push FlowFuse Device Agent container
-        uses: docker/build-push-action@v6.7.0
+        uses: docker/build-push-action@v6.9.0
         with:
           context: docker
           file: docker/Dockerfile
@@ -94,7 +94,7 @@ jobs:
           username: flowforge
           password: ${{ secrets.DOCKER_HUB_PASSWORD_FLOWFORGE }}
       - name: Build and push FlowFuse Device Agent container
-        uses: docker/build-push-action@v6.7.0
+        uses: docker/build-push-action@v6.9.0
         with:
           context: docker
           file: docker/Dockerfile_flowforge