Add workflow concurrency controls to cancel in-progress runs

Prevents multiple workflow runs from the same PR/branch from running simultaneously, saving runner resources and providing faster feedback.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.forgejo/workflows/code-quality.yml

@@ -4,6 +4,10 @@ on:
   pull_request:
     types: [opened, synchronize, reopened]
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   code-quality:
     runs-on: self-hosted