Skip CI run for any change that only contains changes in markdown file (#1310)

* Skip CI run for any change that only contains changes in markdown file

* Only exclude markdown on the top level and everything inside 'Proposals/' path

Author: itingliu

.github/workflows/pull_request.yml

@@ -3,6 +3,9 @@ name: Pull request
 on:
   pull_request:
     types: [opened, reopened, synchronize]
+    paths-ignore:
+      - '*.md'
+      - 'Proposals/**'
 
 jobs:
   tests: