chore: Fix new psalm errors

Signed-off-by: Julius Härtl <jus@bitgrid.net>

lib/Db/AttachmentMapper.php

@@ -31,6 +31,7 @@ use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\IDBConnection;
 use OCP\IUserManager;
 
+/** @template-extends DeckMapper<Attachment> */
 class AttachmentMapper extends DeckMapper implements IPermissionMapper {
 	private $cardMapper;
 	private $userManager;