fix(ci): add concurrency group to queue integration test runs

Prevents overlapping integration test runs on the self-hosted runner.
Uses cancel-in-progress: false so each run completes its full
lifecycle (including cleanup) before the next one starts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/integration-tests.yml

@@ -28,6 +28,10 @@ name: Integration Tests
 # WARNING: Integration tests create and destroy real resources on the target
 # node. Never run against production.
 
+concurrency:
+  group: integration-tests
+  cancel-in-progress: false
+
 on:
   push:
     branches: [ main ]