Fix testCreateOrderEmptyCart: expect 400 after isValidCart refactor

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Controller/OrderControllerTest.php

@@ -106,7 +106,7 @@ class OrderControllerTest extends WebTestCase
         [$event] = $this->createEventWithBillet($em, $user);
 
         $client->request('POST', '/evenement/'.$event->getId().'/commander', [], [], ['CONTENT_TYPE' => 'application/json'], '[]');
-        self::assertResponseIsSuccessful();
+        self::assertResponseStatusCodeSame(400);
 
         $data = json_decode($client->getResponse()->getContent(), true);
         self::assertArrayHasKey('redirect', $data);