又添加setup，尝试多平台构建

.gitea/workflows/build-push.yml

@@ -22,12 +22,20 @@ jobs:
         name: Set up QEMU
         uses: docker/setup-qemu-action@v3
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+        with:
+          driver: docker-container
+          platforms: linux/amd64,linux/arm64
+          install: true
+
       -
         name: Build and push
         uses: docker/build-push-action@v6
         with:
           context: ./backend
           file: ./backend/dockerfile
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: gitea.zfxt.top/zfxt/test:v1.0