Mark hot_mode_dev_cycle_macos_target__benchmark unflaky (#161000)

Should have been marked unflaky when
flutter/flutter#158568 was closed.

Co-authored-by: Chris Bracken <chris@bracken.jp>

Author: jmagman

.ci.yaml

@@ -5047,7 +5047,6 @@ 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: