Updating cirrus docker to use Ubuntu image. (#110351)
Updating cirrus docker to use Ubuntu image. (#110351)

* Updating cirrus docker to use Ubuntui image.

Bug:https://github.com/flutter/flutter/issues/110295

* Update Dockerfile
tvolkert/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter