adds proxy to build.

.github/workflows/ci.yml

@@ -50,6 +50,9 @@ jobs:
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v2
         with:       
+          config-inline: |
+            [registry."docker.io"]
+              mirrors = ["${{ secrets.DOCKERHUB_PROXY_HOSTNAME }}"]
           driver-opts: |
             network=host
           buildkitd-flags: |