Update docker/setup-buildx-action digest to 56a16b8

Author: renovate[bot]

.github/workflows/docker-publish.yml

@@ -48,7 +48,7 @@ jobs:
 
       # Workaround: https://github.com/docker/build-push-action/issues/461
       - name: Setup Docker buildx
-        uses: docker/setup-buildx-action@edfb0fe6204400c56fbfd3feba3fe9ad1adfa345
+        uses: docker/setup-buildx-action@56a16b8f2aa74bcbd3ab9ec13027cd3ac8e3f94f
 
       # Login against a Docker registry except on PR
       # https://github.com/docker/login-action