prevent workflow running twice on PRs from develop into main

Author: akeeste

.github/workflows/main.yml

@@ -1,15 +1,19 @@
 name: Py 3.10, 3.11, 3.12 | Windows Mac Linux
 
 on:
-  push:
+  pull_request:
     branches:
       - main
       - develop
-  pull_request:
+  push:
     branches:
       - main
       - develop
 
+concurrency:
+  group: ${{ github.event.pull_request.number }}  # Use the pull request number as the concurrency group
+  cancel-in-progress: true    # Cancel any in-progress jobs for the same group
+
 jobs:
   set-os:
     runs-on: ubuntu-latest