fix (backend): incorrect database index

Sorry for my silly mistake (cf. 9d56db0fbf 4356099fec)

docs/downgrade.sql

@@ -1,6 +1,7 @@
 BEGIN;
 
 DELETE FROM "migrations" WHERE name IN (
+    'FixNoteUrlIndex1709129810501',
     'RemoveCharts1709047957489',
     'DropUserProfileLanguage1708452631156',
     'EmojiModerator1692825433698',

packages/backend/migration/1709129810501-fix-note-url-index.js

@@ -0,0 +1,11 @@
+export class FixNoteUrlIndex1709129810501 {
+	name = "FixNoteUrlIndex1709129810501";
+
+	async up(queryRunner) {
+		await queryRunner.query(`DROP INDEX "IDX_note_url"`);
+		await queryRunner.query(`CREATE INDEX "IDX_note_url" ON "note" ("url")`);
+	}
+	async down(queryRunner) {
+		/* You don't revert this migration */
+	}
+}