Fix sql syntax error introduced in last commit

SQL/mysql/2020020101.sql

@@ -13,9 +13,9 @@ ALTER TABLE `searches` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_
 ALTER TABLE `filestore` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
 ALTER TABLE `system` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
 
-ALTER TABLE `users` ALTER `username` varchar(128) BINARY NOT NULL;
-ALTER TABLE `cache` ALTER `cache_key` varchar(128) BINARY NOT NULL;
-ALTER TABLE `cache_shared` ALTER `cache_key` varchar(255) BINARY NOT NULL;
-ALTER TABLE `cache_index` ALTER `mailbox` varchar(255) BINARY NOT NULL;
-ALTER TABLE `cache_thread` ALTER `mailbox` varchar(255) BINARY NOT NULL;
-ALTER TABLE `cache_messages` ALTER `mailbox` varchar(255) BINARY NOT NULL;
+ALTER TABLE `users` CHANGE `username` `username` varchar(128) BINARY NOT NULL;
+ALTER TABLE `cache` CHANGE `cache_key` `cache_key` varchar(128) BINARY NOT NULL;
+ALTER TABLE `cache_shared` CHANGE `cache_key` `cache_key` varchar(255) BINARY NOT NULL;
+ALTER TABLE `cache_index` CHANGE `mailbox` `mailbox` varchar(255) BINARY NOT NULL;
+ALTER TABLE `cache_thread` CHANGE `mailbox` `mailbox` varchar(255) BINARY NOT NULL;
+ALTER TABLE `cache_messages` CHANGE `mailbox` `mailbox` varchar(255) BINARY NOT NULL;