chore(deps): update docker/build-push-action action to v6.15.0

Author: renovate[bot]

.github/workflows/update-docker-images.yml

@@ -34,7 +34,7 @@ jobs:
           registry: ghcr.io
           username: ${{github.repository_owner}}
           password: ${{secrets.GITHUB_TOKEN}}
-      - uses: docker/build-push-action@0adf9959216b96bec444f325f1e493d4aa344497 # v6.14.0
+      - uses: docker/build-push-action@471d1dc4e07e5cdedd4c2171150001c434f0b7a4 # v6.15.0
         with:
           context: test
           file: test/docker/${{matrix.dist}}/Dockerfile