Summary:
This PR only fixes a little typo that I noticed working on the documentation of React Native website taking reference from this source code, and then saw it 😅
## Changelog
[General] [Fixed] - Fixed typo from `inly` to `only` inside `Modal.js` library code.
Pull Request resolved: https://github.com/facebook/react-native/pull/28057
Test Plan: Not needed.
Reviewed By: cpojer
Differential Revision: D20197178
Pulled By: TheSavior
fbshipit-source-id: 372f263a16a2de665ced7c0d3f10e3897777d19f