use correct has to label hermes cache key (#45061)

Summary:
This incorrectly used the SHA from facebook/react-native instead of
facebook/hermes to label the hermes cache key. This would bloat our
cache by ~ 1.2GB for each PR.

Changelog: [Internal]

Pull Request resolved: https://github.com/facebook/react-native/pull/45061

Test Plan: We should remove the existing entries for v4-hermes and track the growth over time.

Reviewed By: cipolleschi

Differential Revision: D58780475

Pulled By: blakef

fbshipit-source-id: 0f192faa287f53154f1c8319be6783820d614018