Merge pull request #651 from bwlang/cancel_same_branch_actions

only build the most recent commit on a branch

Author: sfchen

.github/workflows/ci.yml

@@ -3,6 +3,11 @@ on:
   pull_request:
     branches:
       - master
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     strategy: