Marks Windows flutter_packaging_test to be unflaky (flutter#123240)

Marks Windows flutter_packaging_test to be unflaky

Author: fluttergithubbot

.ci.yaml

@@ -4896,7 +4896,6 @@ targets:
   - name: Windows flutter_packaging_test
     recipe: packaging/packaging
     timeout: 60
-    bringup: true
     properties:
       task_name: flutter_packaging
       tags: >