Marks Mac_pixel_7pro native_assets_android to be flaky (flutter#148403)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Mac_pixel_7pro native_assets_android"
}
-->
Issue link: flutter#148402

Author: fluttergithubbot

.ci.yaml

@@ -4313,6 +4313,7 @@ targets:
       task_name: microbenchmarks
 
   - name: Mac_pixel_7pro native_assets_android
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/148402
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60