Update samples by using stable version of Flutter

[larmcr]

First at all, thanks for this fork.

Second, I updated all the samples by using the latest stable version of Flutter:

• Flutter 3.0.5 • channel stable • https://github.com/flutter/flutter.git
• Framework • revision f1875d570e (4 weeks ago) • 2022-07-13 11:24:16 -0700
• Engine • revision e85ea0e79c
• Tools • Dart 2.17.6 • DevTools 2.12.2

In summary:

• Update the YML to use the version of Dart (2.17.x) included in Flutter
• Comment all the backgroundColor fields
• Cast the Object to specific type (int, String or Gender)

I tested it in MacOS (Big Sur 11.6.8, x86_64) and Linux (Kubuntu 22.04, x86_64). Notice that still some errors are shown in the Console/Terminal during execution.

[boroskoyo]

thank you for your collab!