chore(docs): update import for @testing-library/react support (gatsby…

…js#14531)

## Description

`react-testing-library` recently moved to `@testing-library/react`

This PR fixes the docs to match the newly updated version.

docs/docs/testing-react-components.md

@@ -15,7 +15,7 @@ It provides light utility functions on top of `react-dom` and `react-dom/test-ut
 Install the library as one of your project's `devDependencies`. Optionally you may install `jest-dom` to use its [custom jest matchers](https://github.com/gnapse/jest-dom#custom-matchers).
 
 ```shell
-npm install --save-dev react-testing-library jest-dom
+npm install --save-dev @testing-library/react jest-dom
 ```
 
 Create the file `setup-test-env.js` at the root of your project. Insert this code into it:
@@ -24,7 +24,7 @@ Create the file `setup-test-env.js` at the root of your project. Insert this cod
 import "jest-dom/extend-expect"
 
 // this is basically: afterEach(cleanup)
-import "react-testing-library/cleanup-after-each"
+import "@testing-library/react/cleanup-after-each"
 ```
 
 This file gets run automatically by Jest before every test and therefore you don't need to add the imports to every single test file.
@@ -39,11 +39,11 @@ module.exports = {
 
 ## Usage
 
-Let's create a little example test using the newly added library. If you haven't done already read the [unit testing guide](/docs/unit-testing) — essentially you'll use `react-testing-library` instead of `react-test-renderer` now. There are a lot of options when it comes to selectors, this example chooses `getByTestId` here. It also utilizes `toHaveTextContent` from `jest-dom`:
+Let's create a little example test using the newly added library. If you haven't done already read the [unit testing guide](/docs/unit-testing) — essentially you'll use `@testing-library/react` instead of `react-test-renderer` now. There are a lot of options when it comes to selectors, this example chooses `getByTestId` here. It also utilizes `toHaveTextContent` from `jest-dom`:
 
 ```js
 import React from "react"
-import { render } from "react-testing-library"
+import { render } from "@testing-library/react"
 
 // You have to write data-testid
 const Title = () => <h1 data-testid="hero-title">Gatsby is awesome!</h1>