Make sure that build_npm_package waits for react-native-core prebuilds (#51956)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/51956

While working on landing the prebuild for React Native core in CI, I forgot to add a strong dependency between the build_npm_package job and the prebuild_react_native_core job in the workflow.

It was still technically working, because there are other jobs that are slower than building react_native_core that will delay built_npm_package for enough time, but this fix will make it more robust.

## Changelog:
[Internal] -

Reviewed By: cortinico

Differential Revision: D76423766

fbshipit-source-id: 76d91901d63e95add62f26bbff4de0278e8609e3