Add a unique key to the notifications widget so they don't get reparented (#8867)

* Add a unique key to the notifications widget so they don't get reparented

packages/devtools_app/lib/src/framework/notifications_view.dart

diff --git a/packages/devtools_app/lib/src/framework/notifications_view.dart b/packages/devtools_app/lib/src/framework/notifications_view.dart
index 9b1b8c3..3e5f66a 100644
--- a/packages/devtools_app/lib/src/framework/notifications_view.dart
+++ b/packages/devtools_app/lib/src/framework/notifications_view.dart
@@ -172,7 +172,8 @@
 }
 
 class _Notification extends StatefulWidget {
-  const _Notification({required this.message, required this.remove});
+  _Notification({required this.message, required this.remove})
+    : super(key: UniqueKey());
 
   final NotificationMessage message;
   final void Function(_Notification) remove;