Marks Mac_x64_ios hot_mode_dev_cycle_ios__benchmark to be unflaky (#142597)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Mac_x64_ios hot_mode_dev_cycle_ios__benchmark"
}
-->
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_x64_ios%20hot_mode_dev_cycle_ios__benchmark%22).
This test can be marked as unflaky.

.ci.yaml

@@ -4735,7 +4735,6 @@ targets:
   - name: Mac_x64_ios hot_mode_dev_cycle_ios__benchmark
     recipe: devicelab/devicelab_drone
     presubmit: false
-    bringup: true
     timeout: 60
     properties:
       device_os: iOS-16|iOS-17