Add a top-level concurrency block so obsolete runs are auto-cancelled:

.github/workflows/bun-ci.yml

@@ -1,5 +1,9 @@
 name: Bun CI
 
+concurrency:
+  group: bun-ci-${{ github.ref }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: [main]