fix(UserTrait): Fix backend initialization

Signed-off-by: provokateurin <kate@provokateurin.de>

Author: provokateurin

tests/lib/Traits/UserTrait.php

@@ -8,13 +8,16 @@
 namespace Test\Traits;
 
 use OC\User\User;
+use OCP\EventDispatcher\IEventDispatcher;
 use OCP\IUser;
+use OCP\Server;
 
 class DummyUser extends User {
 	private string $uid;
 
 	public function __construct(string $uid) {
 		$this->uid = $uid;
+		parent::__construct($uid, null, Server::get(IEventDispatcher::class));
 	}
 
 	public function getUID(): string {