Bump flutter_scene version

Author: domesticmouse

intro_flutter_gpu/step_12/pubspec.yaml

@@ -9,8 +9,8 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  flutter_scene: ^0.7.0-0
-  flutter_scene_importer: ^0.7.0-0
+  flutter_scene: ^0.8.0-0
+  flutter_scene_importer: ^0.8.0-0
   native_assets_cli: ^0.9.0
   vector_math: ^2.1.4
   xml: ^6.5.0