Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/45475

Instead of zipping all the RNTester's APK together, let's
upload them per buildVariant so it's easier to retrieve them later.

Changelog:
[Internal] [Changed] - Split the rntester APK artifacts in 4

Reviewed By: cipolleschi

Differential Revision: D59809721

fbshipit-source-id: 2d375475d5cee71c212f4d1f3a4a9edf3442358f