Bump docker/build-push-action from 5 to 6 in the dependencies group

Bumps the dependencies group with 1 update: [docker/build-push-action](https://github.com/docker/build-push-action).


Updates `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
  dependency-group: dependencies
...

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

.github/workflows/docker.yml

@@ -32,7 +32,7 @@ jobs:
           images: ${{ env.REGISTRY }}/riichi/kcc3-web
 
       - name: Build and push Docker image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: .
           push: true
@@ -63,7 +63,7 @@ jobs:
           images: ${{ env.REGISTRY }}/riichi/kcc3-proxy
 
       - name: Build and push Docker image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: nginx/
           push: true