Fix typo (#19402)

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

@@ -27,7 +27,7 @@ class _FocusScopeMarker extends InheritedWidget {
 /// The focus tree keeps track of which widget is the user's current focus. The
 /// focused widget often listens for keyboard events.
 ///
-/// The a focus scope does not itself receive focus but instead helps remember
+/// A focus scope does not itself receive focus but instead helps remember
 /// previous focus states. A scope is currently active when its [node] is the
 /// first focus of its parent scope. To activate a [FocusScope], either use the
 /// [autofocus] property or explicitly make the [node] the first focus in the