Marks Mac_arm64_ios basic_material_app_ios__compile to be unflaky (#142594)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Mac_arm64_ios basic_material_app_ios__compile"
}
-->
The test has been passing for [50 consecutive runs](https://data.corp.google.com/sites/flutter_infra_metrics_datasite/flutter_check_test_flakiness_status_dashboard/?p=BUILDER_NAME:%22Mac_arm64_ios%20basic_material_app_ios__compile%22).
This test can be marked as unflaky.

.ci.yaml

@@ -4236,7 +4236,6 @@ targets:
 
   - name: Mac_arm64_ios basic_material_app_ios__compile
     recipe: devicelab/devicelab_drone
-    bringup: true
     presubmit: false
     timeout: 60
     properties: