Marks Mac_arm64_ios hot_mode_dev_cycle_ios__benchmark to be flaky (flutter#158242)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Mac_arm64_ios hot_mode_dev_cycle_ios__benchmark"
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-->
Issue link: flutter#158241

Author: fluttergithubbot

.ci.yaml

@@ -5212,6 +5212,7 @@ targets:
       task_name: hot_mode_dev_cycle_ios__benchmark
 
   - name: Mac_arm64_ios hot_mode_dev_cycle_ios__benchmark
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/158241
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60