ci: add actions/labeler

Author: peaceiris

.github/workflows/labeler.yml

@@ -0,0 +1,13 @@
+name: "Pull Request Labeler"
+# https://github.com/actions/labeler
+
+on:
+ - pull_request_target
+
+jobs:
+ triage:
+ runs-on: ubuntu-18.04
+ steps:
+ - uses: actions/labeler@v3
+ with:
+ repo-token: "${{ secrets.GH_PAT }}"