Ensure that the artifacts have the right extension (#49755)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/49755

The artifacts are uploaded without the .tar.gz extension and the gradle script fails to upload them to sonatype.

This change adds the extensions.

## Changelog:
[Internal] -

Reviewed By: sammy-SC

Differential Revision: D70443149

fbshipit-source-id: c16d1842688b82ac216ffb90ecf2b75f562cca64