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] <[email protected]>

Author: dependabot[bot]

.github/workflows/build-docker-image.yml

@@ -36,7 +36,7 @@ jobs:
               type=sha
 
         - name: Build and Push
-          uses: docker/build-push-action@v5
+          uses: docker/build-push-action@v6
           with:
             context: ./backend/nginx
             cache-from: type=gha
@@ -70,7 +70,7 @@ jobs:
               type=sha
 
         - name: Build and Push
-          uses: docker/build-push-action@v5
+          uses: docker/build-push-action@v6
           with:
             context: ./backend
             cache-from: type=gha