docker.yml: fix yaml syntax

.github/workflows/docker.yml

@@ -32,9 +32,9 @@ jobs:
           echo "${DOCKER_PASSWORD}" | docker login --username "${DOCKER_USERNAME}" --password-stdin
 
       - name: Docker buildx image and push on master branch
-      if: github.ref == 'refs/heads/master'
-      run: |
-        docker buildx build --output "type=image,push=true" --platform=linux/amd64,linux/arm/v7,linux/arm64 --tag xjasonlyu/tun2socks:latest .
+        if: github.ref == 'refs/heads/master'
+        run: |
+          docker buildx build --output "type=image,push=true" --platform=linux/amd64,linux/arm/v7,linux/arm64 --tag xjasonlyu/tun2socks:latest .
 
       - name: Replace tag without `v`
         if: startsWith(github.ref, 'refs/tags/')