Marks Mac_ios external_ui_integration_test_ios to be unflaky (#106041)

Author: fluttergithubbot

.ci.yaml

@@ -3233,7 +3233,6 @@ targets:
     scheduler: luci
 
   - name: Mac_ios external_ui_integration_test_ios
-    bringup: true # Flaky https://github.com/flutter/flutter/issues/103057
     recipe: devicelab/devicelab_drone
     presubmit: false
     timeout: 60