Updated incorrect file name in documentation (#11566)

In the
last code snippet of page `App Architecture -> Architecture case study
-> UI layer` document, the last code snippet's current title is
`home_viewmodel.dart` which should be `home_screen.dart`. Here's a link
to the document- [UI layer |
Flutter](https://docs.flutter.dev/app-architecture/case-study/ui-layer).

src/content/app-architecture/case-study/ui-layer.md

@@ -578,7 +578,7 @@ the view wants to render. This gets at *why* the Compass app uses `Commands`.
 In the view's `Widget.build` method,
 the command is used to conditionally render different widgets.
 
-```dart title=home_viewmodel.dart
+```dart title=home_screen.dart
 // ...
 child: ListenableBuilder(
   listenable: [!viewModel.load!],