update notification tab data when clicking on navigation bars

lib/view_models/tenders_view_model.dart

@@ -126,6 +126,8 @@ class TendersViewModel with ChangeNotifier {
   }
 
   void init(BuildContext context) async {
+    _isLoading = true;
+    notifyListeners();
     clearAll();
     await getTenders(context: context);
   }