Fix invalid markdown lang (#42442)

x-ref: [slack
thread](https://vercel.slack.com/archives/C02F56A54LU/p1667507770684919)

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Author: ijjk

docs/basic-features/font-optimization.md

@@ -91,17 +91,18 @@ export default function MyApp({ Component, pageProps }) {
 
 To use the font on a single page, add it to the specific page as shown below:
 
-```js:pages/index.js
-import { Inter } from '@next/font/google';
+```js
+// pages/index.js
+import { Inter } from '@next/font/google'
 
-const inter = Inter();
+const inter = Inter()
 
 export default function Home() {
   return (
     <div className={inter.className}>
       <p>Hello World</p>
     </div>
-  );
+  )
 }
 ```