[deps]: Update docker/build-push-action action to v6 (#267)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

.github/workflows/build-unified.yml

@@ -146,7 +146,7 @@ jobs:
           path: 'server'
 
       - name: Build and push Docker image
-        uses: docker/build-push-action@ca052bb54ab0790a636c9b5f226502c73d547a25 # v5.4.0
+        uses: docker/build-push-action@31159d49c0d4756269a0940a750801a1ea5d7003 # v6.1.0
         with:
           context: .
           file: docker-unified/Dockerfile