Bump docker/build-push-action from 6.13.0 to 6.15.0 (#479)

Author: dependabot[bot]

.github/workflows/docker-testing.yml

@@ -37,7 +37,7 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@f7ce87c1d6bead3e36075b2ce75da1f6cc28aaca # v3.9.0
       - name: Build Docker image (no push)
-        uses: docker/build-push-action@ca877d9245402d1537745e0e356eab47c3520991 # v6.13.0
+        uses: docker/build-push-action@471d1dc4e07e5cdedd4c2171150001c434f0b7a4 # v6.15.0
         with:
           context: .
           file: "Dockerfile"