chore(ci): add concurrency to cancel in-progress workflow runs

- Prevents duplicate CI runs on the same branch
- Ensures only the latest commit triggers the test job

Author: koki-develop

.github/workflows/ci.yml

@@ -8,6 +8,10 @@ on:
     branches:
       - main
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   test:
     name: Test