Marks Mac_benchmark flutter_gallery_macos__compile to be flaky (#160496)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Mac_benchmark flutter_gallery_macos__compile"
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Issue link: flutter/flutter#160495

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

Author: fluttergithubbot

.ci.yaml

@@ -3986,6 +3986,7 @@ targets:
       task_name: flavors_test_macos
 
   - name: Mac_benchmark flutter_gallery_macos__compile
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/160495
     presubmit: false
     recipe: devicelab/devicelab_drone
     timeout: 60