fix

https://github.com/misskey-dev/misskey/commit/d53795184cd0ee326b0da58b267e3460f948703c#r62707827

packages/backend/src/server/proxy/proxy-media.ts

@@ -19,6 +19,7 @@ export async function proxyMedia(ctx: Koa.Context) {
 
 		const { mime, ext } = await detectType(path);
 
+		if (!mime.startsWith('image/')) throw 403;
 		if (!FILE_TYPE_BROWSERSAFE.includes(mime)) throw 403;
 
 		let image: IImage;