set title of username double notification based on if it's a new user

src/Controller/AdminController.php

@@ -37,7 +37,7 @@ class AdminController extends AbstractController
         if($request->request->get('username') != $user->getUsername()) {
             if ($users->findOneBy(['username' => $request->request->get('username') ])) {
                 $this->addFlash('notice', [
-                    'title'=> 'Failed to change username',
+                    'title'=>  $user->getUsername() ? 'Failed to change username' : 'Failed to create user',
                     'message' => 'The new username for this user is already in use, please try a different username.'
                 ]);