Update docker/setup-buildx-action digest to a56031a

Author: renovate[bot]

.github/workflows/docker-publish.yml

@@ -46,7 +46,7 @@ jobs:
 
       # Workaround: https://github.com/docker/build-push-action/issues/461
       - name: Setup Docker buildx
-        uses: docker/setup-buildx-action@8c0edbc76e98fa90f69d9a2c020dcb50019dc325
+        uses: docker/setup-buildx-action@a56031a493fd4c638a1ace23e03793012b196e65
 
       # Login against a Docker registry except on PR
       # https://github.com/docker/login-action