Update wrong code snippet (#34520)

Following the [example](https://nextjs.org/docs/advanced-features/custom-document), avoiding the following error:
>  Identifier 'Document' has already been declared



## Bug

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

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

errors/no-stylesheets-in-head-component.md

@@ -18,7 +18,7 @@ Add the stylesheet in a custom `Document` component.
 
 ```jsx
 // pages/_document.js
-import Document, { Html, Head, Main, NextScript } from 'next/document'
+import { Html, Head, Main, NextScript } from 'next/document'
 
 export default function Document() {
   return (