Marks Mac_x64 hot_mode_dev_cycle_macos_target__benchmark to be flaky (#158569)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
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  "name": "Mac_x64 hot_mode_dev_cycle_macos_target__benchmark"
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Issue link: flutter/flutter#158568

Author: fluttergithubbot

.ci.yaml

@@ -4896,6 +4896,7 @@ targets:
       task_name: hello_world_ios__compile
 
   - name: Mac_x64 hot_mode_dev_cycle_macos_target__benchmark
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/158568
     recipe: devicelab/devicelab_drone
     timeout: 60
     properties: