ci: use --concurrency 1 to run tests serially and avoid interference

Author: MBanucu

.github/workflows/ci.yml

@@ -48,7 +48,7 @@ jobs:
         run: bun run build:all:prod
 
       - name: Run tests
-        run: bun test
+        run: bun test --concurrency 1
 
   dependency-review:
     runs-on: ubuntu-24.04