RNGP: Read `enableWarningsAsErrors` property correctly (#46657)

Summary:
I've noticed that some users are reporting build failures due to warnings inside RNGP.
We do have `allWarningsAsErrors` set to true for everyone (also for users).
That's too aggressive, and can cause build failures which are not necessary. Let's keep it enabled only on our CI (when the `enableWarningsAsErrors` property is set).

## Changelog:

[INTERNAL] - RNGP: Read `enableWarningsAsErrors` property correctly

Pull Request resolved: https://github.com/facebook/react-native/pull/46657

Test Plan: CI

Reviewed By: NickGerleman

Differential Revision: D63459601

Pulled By: cortinico

fbshipit-source-id: 0307e8d6771518038a5abe27ca5a993cb0a9f8c0