Only cancel in progress workflow runs for pull requests

Author: mcbarton

.github/workflows/main.yml

@@ -13,7 +13,7 @@ on:
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
-  cancel-in-progress: true
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   build: