Update docker/build-push-action digest to a3f8b56

Author: renovate[bot]

.github/workflows/ghcr-io-docker-build.yaml

@@ -60,7 +60,7 @@ jobs:
       # https://github.com/docker/build-push-action
       - name: Build and Push Jenkins image
         id: build-and-push
-        uses: docker/build-push-action@48aba3b46d1b1fec4febb7c5d0c644b249a11355
+        uses: docker/build-push-action@a3f8b56eb84ab0706abf5bce25158b9c29d01727
         with:
           context: .
           file: docker/Dockerfile