only run latest workflow for pull requests (#480)

- Add concurrency group configuration to CI workflow
- Cancel in-progress jobs for pull requests only
- Keep all workflow runs for main branch pushes and tags
- Optimize CI pipeline resource usage

Author: schroedtert

.github/workflows/ci.yml

@@ -15,6 +15,10 @@ on:
       - main
       - rls-*
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.event.pull_request.number || github.sha }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 permissions:
   contents: write