Merge pull request #61411 from nextcloud/backport/58813/stable33

[stable33] test(ldap): align expectation for unset `ldapUserDisplayName2` with implementation to avoid PHP 8.5 warning

Author: AndyScherzinger

apps/user_ldap/tests/AccessTest.php

@@ -708,7 +708,7 @@ public function testUserStateUpdate(): void {
 			->method('__get')
 			->willReturnMap([
 				[ 'ldapUserDisplayName', 'displayName' ],
-				[ 'ldapUserDisplayName2', null],
+				[ 'ldapUserDisplayName2', ''],
 			]);
 
 		$offlineUserMock = $this->createMock(OfflineUser::class);