Kill previous CI jobs when new pushed

.github/workflows/docs.yml

@@ -8,6 +8,10 @@ on:
     branches:
       - master
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-deploy:
     runs-on: ubuntu-latest