fix filtering of quote uri

apparently filtering with `x => x !== null` will let `undefined`
through…

packages/backend/src/core/activitypub/models/ApNoteService.ts

@@ -483,7 +483,7 @@ export class ApNoteService {
 				}
 			};
 
-			const uris = unique([note._misskey_quote, note.quoteUrl, note.quoteUri].filter(x => x !== null));
+			const uris = unique([note._misskey_quote, note.quoteUrl, note.quoteUri].filter(x => x != null));
 			const results = await Promise.all(uris.map(tryResolveNote));
 
 			quote = results.filter((x): x is { status: 'ok', res: MiNote } => x.status === 'ok').map(x => x.res).at(0);