ci: Add GH workflow for syncing labels

.github/workflows/sync-labels.yml

@@ -0,0 +1,17 @@
+name: Sync labels
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - .github/labels.yml
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: micnncim/action-label-syncer@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          manifest: .github/labels.yml