restore missing use statement

Author: xabbuh

Tests/EventListener/SessionListenerTest.php

@@ -14,6 +14,7 @@
 use PHPUnit\Framework\TestCase;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\Container;
+use Symfony\Component\DependencyInjection\ServiceLocator;
 use Symfony\Component\HttpFoundation\Cookie;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpFoundation\RequestStack;