fix: platform_dispatcher documentation typo (flutter#41739)

fixes [https://github.com/flutter/flutter/issues/126082](https://github.com/flutter/flutter/issues/126082) 

*If you had to change anything in the [flutter/tests] repo, include a link to the migration guide as per the [breaking change policy].*

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: Mayb3Nots

lib/ui/platform_dispatcher.dart

@@ -115,7 +115,7 @@ class PlatformDispatcher {
 
   /// The [PlatformDispatcher] singleton.
   ///
-  /// Consider avoiding static references to this singleton though
+  /// Consider avoiding static references to this singleton through
   /// [PlatformDispatcher.instance] and instead prefer using a binding for
   /// dependency resolution such as `WidgetsBinding.instance.platformDispatcher`.
   ///