move migration to correct script

Fixes: https://pagure.io/koji/issue/2521

docs/schema-upgrade-1.22-1.23.sql

@@ -6,6 +6,7 @@ BEGIN;
 
 CREATE INDEX task_by_no_parent_state_method ON task(parent, state, method) WHERE parent IS NULL;
 
+ALTER TABLE tag_extra ALTER COLUMN value DROP NOT NULL;
 
 -- Message queue for the protonmsg plugin
 CREATE TABLE proton_queue (

docs/schema-upgrade-1.23-1.24.sql

@@ -1,9 +0,0 @@
--- upgrade script to migrate the Koji database schema
--- from version 1.23 to 1.24
-
-
-BEGIN;
-
-ALTER TABLE tag_extra ALTER COLUMN value DROP NOT NULL;
-
-COMMIT;