fix: add conditional checks for facebook/react-native repo for nightly (#53700)

Summary:
This PR adds additional checks to run nightly jobs only on the main repo.

I noticed pretty heavy usage on my fork of React Native:

<img width="951" height="179" alt="Screenshot 2025-09-10 at 11 47 29" src="https://github.com/user-attachments/assets/91cb9e4a-8658-42bd-bbfe-ffba01b0b3b3" />

I also noticed a typo in this file with output instead of outputs

## Changelog:

[INTERNAL] [FIXED] - add conditional checks for facebook/react-native repo for nightly workflow

Pull Request resolved: https://github.com/facebook/react-native/pull/53700

Test Plan: Check if the syntax is correct.

Reviewed By: cortinico

Differential Revision: D82104958

Pulled By: cipolleschi

fbshipit-source-id: fc2e6e0299345ebd115c7a574a5a8161f2b0ca5c