Update docker/build-push-action action to v6.9.0 (#391)

| datasource  | package                  | from   | to     |
| ----------- | ------------------------ | ------ | ------ |
| github-tags | docker/build-push-action | v6.7.0 | v6.9.0 |

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

Author: renovate[bot]

.github/workflows/ci.yml

@@ -72,7 +72,7 @@ jobs:
         uses: docker/setup-buildx-action@988b5a0280414f521da01fcc63a27aeeb4b104db # v3.6.1
 
       - name: Build Plus Docker Image
-        uses: docker/build-push-action@5cd11c3a4ced054e52742c5fd54dca954e0edd85 # v6.7.0
+        uses: docker/build-push-action@4f58ea79222b3b9dc2c8bbdd6debcef730109a75 # v6.9.0
         with:
           file: docker/Dockerfile
           tags: nginx-plus