tests(docs.yml): cancel workflow if head is updated

Author: jcs090218

.github/workflows/docs.yml

@@ -13,6 +13,10 @@ on:
       - master
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   publish-doc:
     runs-on: ubuntu-latest