Fix: Punycodeなインスタンスが重複登録される (#4667)

src/services/register-or-fetch-instance-doc.ts

@@ -1,9 +1,12 @@
 import Instance, { IInstance } from '../models/instance';
 import federationChart from '../services/chart/federation';
+import { toDbHost } from '../misc/convert-host';
 
 export async function registerOrFetchInstanceDoc(host: string): Promise<IInstance> {
 	if (host == null) return null;
 
+	host = toDbHost(host);
+
 	const index = await Instance.findOne({ host });
 
 	if (index == null) {