rename App-test.tsx to App.test.tsx (#35826)

Summary:
The starter test file when creating a `create-react-app` project is `App.test.js`, while in react-native its `App-test.js`_(recently changed to `.tsx` instead of `.js`)_

This aims to unify the naming convention between `create-react-app` and `react-native init`.

Originally suggested here: react-native-community/discussions-and-proposals#570

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[GENERAL] [CHANGED] - Renamed App-test.tsx to App.test.tsx to unify naming convention with create-react-app

Pull Request resolved: #35826

Test Plan:
1. cd template
2. yarn
3. yarn test

The test inside `__tests__/App.test.tsx` should (still) pass

Reviewed By: cipolleschi

Differential Revision: D42527535

Pulled By: NickGerleman

fbshipit-source-id: 5247c5a65760973afe39a4b37abb5a6b52c1fadc