build(deps): bump docker/build-push-action from 5 to 6

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

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

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

.github/workflows/webapp-docker-release-on-tag-docker-hub.yml

@@ -46,7 +46,7 @@ jobs:
 
       - name: Build and push ${{ steps.pushtags.outputs.tag }}
         id: docker_build
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./starsky
           platforms: linux/amd64,linux/arm64,linux/arm/v7

.github/workflows/webapp-unstable-docker-buildx.yml

@@ -58,7 +58,7 @@ jobs:
 
       - name: Build and push master
         id: docker_build_push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         if: github.event_name != 'pull_request'
         with:
           context: ./starsky
@@ -70,7 +70,7 @@ jobs:
 
       - name: Build and don't push
         id: docker_build_pull_request
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         if: github.event_name == 'pull_request'
         with:
           context: ./starsky