ci: only cancel previous PR runs on Forgejo Actions

Author: alexrp

.forgejo/workflows/ci.yaml

@@ -7,7 +7,7 @@ on:
   workflow_dispatch:
 concurrency:
   group: ${{ github.head_ref || github.run_id }}-${{ github.actor }}
-  cancel-in-progress: true
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 permissions:
   contents: read
 jobs: