Do not use hermesNightly on the release branch (#55890)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55890

Changelog: [Internal]

This was done manually on `0.84-stable` and `0.85-stable`.

Discovered due to the failure when pushing the new `0.85-stable` branch:
https://github.com/facebook/react-native/actions/runs/22592250332/job/65471130298.

Reviewed By: cortinico

Differential Revision: D95051387

fbshipit-source-id: 2a9f0cfeef37ec1903d42259bec3518af721410c