Update flet dependency override to 'sensors' ref

Changed the flet package git reference from 'sensors-brightness' to 'sensors' in pubspec.yaml to use the updated branch.

{{cookiecutter.out_dir}}/pubspec.yaml

@@ -28,7 +28,7 @@ dependency_overrides:
   flet:
     git:
       path: packages/flet
-      ref: sensors-brightness
+      ref: sensors
       url: https://github.com/flet-dev/flet.git
 
   serious_python: 0.9.6