🔥 clean: Update 404.tsx (#6132)

https://ant.design/components/result-cn/#components-result-demo-404
文档上status是字符串，会报错

src/pages/404.tsx

@@ -4,7 +4,7 @@ import { router } from 'umi';
 
 const NoFoundPage: React.FC<{}> = () => (
   <Result
-    status={404}
+    status="404"
     title="404"
     subTitle="Sorry, the page you visited does not exist."
     extra={