Use Docker buildx in release

Author: adamtheturtle

.github/workflows/release.yml

@@ -81,6 +81,16 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+        with:
+          # This defaults to "docker-containerized".
+          # We want to share the vws-mock:base image to the building of the
+          # later builds, without pushing to a registry.
+          #
+          # Therefore, we choose not to build in a container.
+          driver: docker
+
       - name: Build base Docker image
         uses: docker/build-push-action@v2.7.0
         with: