fixed doc typo (#7270)

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

@@ -104,7 +104,7 @@ class _FocusScope extends InheritedWidget {
 /// widget in this part of the focus tree. If this Focus widget is the currently
 /// focused subtree of the focus system (i.e., the path from it to the root is
 /// focused at each level and it hasn't focused any of its enclosed Focus
-/// widgets), then the widget this this global key actually has the focus in the
+/// widgets), then the widget with this global key actually has the focus in the
 /// entire system.
 class Focus extends StatefulWidget {
   /// Creates a scope for managing focus.