CI: Cancel prior runs when new run for same PR/branch is started (#940)

.github/workflows/ci.yaml

@@ -6,7 +6,12 @@ on:
     branches: main
   schedule:
   - cron:  '5 0 * * *'
-
+
+# Cancel in progress CI runs when a new run targeting the same PR or branch/tag is triggered.
+# https://stackoverflow.com/questions/66335225/how-to-cancel-previous-runs-in-the-pr-when-you-push-new-commitsupdate-the-curre
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
 
 jobs:
     flake8: