Fix unit tests

Signed-off-by: Joas Schilling <coding@schilljs.com>

apps/provisioning_api/tests/Controller/UsersControllerTest.php

@@ -1486,7 +1486,8 @@ class UsersControllerTest extends TestCase {
 		$targetUser
 			->expects($this->once())
 			->method('setDisplayName')
-			->with('NewDisplayName');
+			->with('NewDisplayName')
+			->willReturn(true);
 		$targetUser
 			->expects($this->any())
 			->method('getUID')