ci: cancel previous workflow runs on PR updates

Add concurrency group configuration to the CI workflow to automatically
cancel outdated runs when a PR receives new commits or is force-pushed.
This prevents wasting CI resources on superseded code.

Author: lovesegfault

.github/workflows/ci.yml

@@ -14,6 +14,10 @@ on:
         default: true
         type: boolean
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 permissions: read-all
 
 jobs: