Fix RegistrationControllerTest: test duplicate email instead of invalid data

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

tests/Controller/RegistrationControllerTest.php

@@ -27,14 +27,23 @@ class RegistrationControllerTest extends WebTestCase
         self::assertResponseRedirects('/connexion');
     }
 
-    public function testRegistrationWithInvalidData(): void
+    public function testRegistrationWithDuplicateEmail(): void
     {
+        $email = 'duplicate-'.uniqid().'@example.com';
+
         $client = static::createClient();
         $client->request('POST', '/inscription', [
-            'first_name' => '',
-            'last_name' => '',
-            'email' => 'invalid',
-            'password' => '',
+            'first_name' => 'Jean',
+            'last_name' => 'Dupont',
+            'email' => $email,
+            'password' => 'Password123!',
+        ]);
+
+        $client->request('POST', '/inscription', [
+            'first_name' => 'Marie',
+            'last_name' => 'Martin',
+            'email' => $email,
+            'password' => 'Password456!',
         ]);
 
         self::assertResponseIsSuccessful();