Fix minor typo (#30353)

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

@@ -596,7 +596,7 @@ class EditableText extends StatefulWidget {
   /// Called when the user initiates a change to the TextField's
   /// value: when they have inserted or deleted text.
   ///
-  /// This callback does run not when the TextField's text is changed
+  /// This callback doesn't run when the TextField's text is changed
   /// programmatically, via the TextField's [controller]. Typically it
   /// isn't necessary to be notified of such changes, since they're
   /// initiated by the app itself.