Marks Windows windowing_test to be flaky (#177716)

<!-- meta-tags: To be used by the automation script only, DO NOT MODIFY.
{
  "name": "Windows windowing_test"
}
-->
Issue link: flutter/flutter#177715

Author: fluttergithubbot

.ci.yaml

@@ -6982,6 +6982,7 @@ targets:
       task_name: windows_startup_test
 
   - name: Windows windowing_test
+    bringup: true # Flaky https://github.com/flutter/flutter/issues/177715
     recipe: devicelab/devicelab_drone
     presubmit: true
     timeout: 60