Bump pubspec.lock

`flutter pub get`

Upgrade to ruby 3

Fastfile: Use `UI.user_error!`, not `raise`

`UI.user_error!` is much more readable for something specific the user
needs to do, so switch over.

Fastfile & Workflow cleanup

- Add comments for various parts of the workflow and Fastfile
- Bump Flutter version
- Allow manual workflow dispatch

Upgrade to ruby 3

Use `fastlane match` for signing in workflow