Use compatible checkin timestamp migration

drizzle/0001_add_checkin_type.sql

@@ -1,2 +1,2 @@
 ALTER TABLE `progress` ADD `checkin_type` text NOT NULL DEFAULT 'normal';
-ALTER TABLE `progress` ADD `checked_at` text NOT NULL DEFAULT CURRENT_TIMESTAMP;
+ALTER TABLE `progress` ADD `checked_at` text NOT NULL DEFAULT '';