Store artifacts only on main and stable branches (#38954)

Summary:
This change stores artifacts in CI only when it runs in main or in a stable branch

## Changelog:

[Internal] - Store CI artifacts only on main or on stable branches

Pull Request resolved: https://github.com/facebook/react-native/pull/38954

Test Plan: CircleCI stays green and we don't store anything on pr branch

Reviewed By: cortinico

Differential Revision: D48267659

Pulled By: cipolleschi

fbshipit-source-id: 6257270948c770e09492691c995cbe84d7a085ac