Clear up info messages from flutter analyze (Flutter beta 3.23 edition)

[cpswan]

Which at_widget package you find issue with?

at_backupkey_flutter, at_common_flutter, at_contacts_group_flutter, at_events_flutter, at_location_flutter, at_login_flutter, at_notify_flutter, at_onboarding_flutter, at_sync_ui_flutter, at_theme_flutter

On what platforms did you experience the issue?

Linux

What version are you using?

Trunk

What happened?

A new Flutter beta (for 3.23) dropped on 6 Jun (just after we cleared up the infos for Flutter 3.22 in #847)

See recent static analysis runs e.g. https://github.com/atsign-foundation/at_widgets/actions/runs/9446898794

Steps to reproduce

1. Go to any of the listed packages
2. Run `flutter analyze` using Flutter 3.23 beta