Improve test stability in CI (#45070)

Summary:
This change splits the build step and the test step for running the test on iOS, so we can introduce a retry for the test only.
We are doing that because we have seen some flakyness in CI jobs as sometimes the simulator fails to install the app.

## Changelog:
[Internal] - Add retry to iOS tests

Pull Request resolved: https://github.com/facebook/react-native/pull/45070

Test Plan: Testing in CircleCI

Reviewed By: cortinico

Differential Revision: D58786706

Pulled By: cipolleschi

fbshipit-source-id: 61363cb86dd1a496d3595b43b6331cbee7f032ea