fix typo of 'not' instead of 'now' for `useInheritedMediaQuery` (#139940)

The doc comment for `useInheritedMediaQuery` has a typo of 'not' instead of 'now' and it is confusing at the `@Deprecated()` message clearly states it is *now* ignored.
(and indeed checking the code you can verify that it *is* indeed ignored)

existing code before PR:
```dart
/// {@template flutter.widgets.widgetsApp.useInheritedMediaQuery}
/// Deprecated. This setting is not ignored.
///                             ^^^
/// The widget never introduces its own [MediaQuery]; the [View] widget takes
/// care of that.
/// {@endtemplate}
@Deprecated(
  'This setting is now ignored. '
  'WidgetsApp never introduces its own MediaQuery; the View widget takes care of that. '
  'This feature was deprecated after v3.7.0-29.0.pre.'
)
final bool useInheritedMediaQuery;
```

- [X ] I read the [Contributor Guide] and followed the process outlined there for submitting PRs.

packages/flutter/lib/src/widgets/app.dart

@@ -1171,7 +1171,7 @@ class WidgetsApp extends StatefulWidget {
   final String? restorationScopeId;
 
   /// {@template flutter.widgets.widgetsApp.useInheritedMediaQuery}
-  /// Deprecated. This setting is not ignored.
+  /// Deprecated. This setting is now ignored.
   ///
   /// The widget never introduces its own [MediaQuery]; the [View] widget takes
   /// care of that.