fix: content_script_version_4.nim: migration failed when dropping une…

…xisting constraing (#2672)

migrations/message_store_postgres/content_script_version_4.nim

@@ -2,7 +2,6 @@ const ContentScriptVersion_4* =
   """
 ALTER TABLE IF EXISTS messages_backup RENAME TO messages;
 ALTER TABLE messages RENAME TO messages_backup;
-ALTER TABLE messages_backup DROP CONSTRAINT messageIndex;
 
 CREATE TABLE IF NOT EXISTS messages (
    pubsubTopic VARCHAR NOT NULL,
@@ -64,6 +63,8 @@ INSERT INTO messages (
                        storedAt
                    FROM messages_backup;
 
+CREATE INDEX IF NOT EXISTS i_query ON messages (contentTopic, pubsubTopic, storedAt, id);
+
 DROP TABLE messages_backup;
 
 UPDATE version SET version = 4 WHERE version = 3;