fix(build): `buildx` setup must be after registry login

.github/workflows/sub-build-docker-image.yml

@@ -120,15 +120,6 @@ jobs:
             type=edge,enable={{is_default_branch}}
             type=schedule
 
-      # Setup Docker Buildx to use Docker Build Cloud
-      - name: Set up Docker Buildx
-        id: buildx
-        uses: docker/setup-buildx-action@v3
-        with:
-          version: "lab:latest"
-          driver: cloud
-          endpoint: "zfnd/zebra"
-
       - name: Authenticate to Google Cloud
         id: auth
         uses: google-github-actions/auth@v2.1.2
@@ -155,6 +146,15 @@ jobs:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
+      # Setup Docker Buildx to use Docker Build Cloud
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v3
+        with:
+          version: "lab:latest"
+          driver: cloud
+          endpoint: "zfnd/zebra"
+
       # Build and push image to Google Artifact Registry, and possibly DockerHub
       - name: Build & push
         id: docker_build