I noticed several issues with the plugin linter script:

https://github.com/flutter/plugins/blob/master/script/lint_darwin_plugins.sh

This script is used by FlutterFire as well:

https://github.com/FirebaseExtended/flutterfire/blob/master/script/lint_darwin_plugins.sh

1. In pre submit checks, script is printing errors on the command line but the exit code is 0: https://cirrus-ci.com/task/5104699145715712
2. The script doesn't do anything on post submit. Probably it should run on all plugins: https://cirrus-ci.com/task/5521154811101184
3. The script seems to be hanging on this PR. See test results for [all] fix for UserAgent.h compilation failures firebase/flutterfire#2099 here:
   https://cirrus-ci.com/task/6400550270926848

Finally, we should probably make this be --verbose instead of --silent so that the reason for failures will be visible in the Cirrus logs.

FYI @jmagman