New jsx transform not applied when running tests after ejecting

[celerytea]

Describe the bug

Getting "React is not defined" when running tests on react-scripts v4.0.1 after ejecting

Steps to reproduce

1. Create a new project
2. Eject
3. Run a test

Actually I also got #6174 so I needed to remove node_modules and rerun yarn, but this is a different issue.

Analysis

Looking at

create-react-app/packages/react-scripts/scripts/utils/createJestConfig.js

Lines 44 to 46 in 9b08e3c

	'^.+\\.(js|jsx|mjs|cjs|ts|tsx)$': isEjecting
	? '<rootDir>/node_modules/babel-jest'
	: resolve('config/jest/babelTransform.js'),

the unejected version runs babelTransform.js while the ejected version runs babel-jest directly, however babelTransform.js is where we set up the new jsx runtime.

Copying babelTransform.js and updating the "transform" key in package.json fixed this issue.

Alternatively updating package.json from

"babel": {
  "presets": [
    "react-app"
  ]
}

to

"babel": {
  "presets": [
    [
      "react-app",
      {
        "runtime": "automatic"
      }
    ]
  ]
}

would also fix this issue.

[maxsbelt]

Should be fixed by #10091.