Bugfix: labeler not work (#3500)

* Bugfix: labeler not work

* Fix yaml file indent

.github/workflows/labeler.yml

 name: Labeler
-  on: 
-    - pull_request
+on: [pull_request]
   
-  jobs:
-    label:
-      runs-on: ubuntu-latest
-      steps:
-        - uses: actions/labeler@v2
-          with:
-            repo-token: "${{ secrets.GITHUB_TOKEN }}"
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/labeler@v2
+        with:
+          repo-token: "${{ secrets.GITHUB_TOKEN }}"