test: add test for new getDisplayUser() method in OC\User\Manager

test: add test for new getDisplayUser() method in OC\User\Manager

Signed-off-by: Kent Delante <kent@delante.me>

Assisted-by: ClaudeCode:claude-sonnet-5

[skip ci]

Author: leftybournes

tests/lib/User/ManagerTest.php

@@ -15,6 +15,7 @@
 use OC\User\User;
 use OCP\Config\IUserConfig;
 use OCP\EventDispatcher\IEventDispatcher;
+use OCP\Federation\ICloudId;
 use OCP\ICache;
 use OCP\ICacheFactory;
 use OCP\IConfig;