Skip the workflow on "skip ci"

Author: nebularg

.github/workflows/build-classic.yml

@@ -15,6 +15,7 @@ env:
 jobs:
   build:
     runs-on: ubuntu-latest
+    if: contains(github.event.head_commit.message, 'skip ci') != true
 
     steps:
       - uses: actions/checkout@v1