Mark smoke_catalina_start_up_ios as flaky (#61737)
Mark smoke_catalina_start_up_ios as flaky (#61737)

https://github.com/flutter/flutter/issues/61736
flutter/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter