Because every version of flutter_test from sdk depends on async 2.8.2 and every version of logger_flutter from git depends on async 2.8.1, flutter_test from sdk is incompatible with logger_flutter from git.
flutter upgrade
Flutter is already up to date on channel stable
Flutter 2.8.1 • channel stable • https://github.com/flutter/flutter.git
Framework • revision 77d935af4d (2 weeks ago) • 2021-12-16 08:37:33 -0800
Engine • revision 890a5fca2e
Tools • Dart 2.15.1
Because every version of flutter_test from sdk depends on async 2.8.2 and every version of logger_flutter from git depends on async 2.8.1, flutter_test from sdk is incompatible with logger_flutter from git.