fixed cp command to work with gnu coreutils (#54063)

Summary:
When using gnu coreutils, installation of ReactNativeDependenices on iOS fails at compile time with errors like in the following issue (in the Expo repo):

https://github.com/expo/expo/issues/38992

This is caused by a missing `.` in the end of the path name that the built-in MacOS cp command handles well, but that will create an extra Headers folder when using cp from gnu coreutils.

This commit fixes this by adding the missing `.`

## Changelog:

[IOS] [FIXED] - Fixed issue when using gnu coreutils cp command when using precompiled binaries causing compilation error

Pull Request resolved: https://github.com/facebook/react-native/pull/54063

Test Plan:
- Verify that you're running gnu coreutils (`cp --version`)
- Create new expo app `npx create-expo-app`
- Build on iOS - should error without this fix, should work with the fix.

Reviewed By: christophpurrer

Differential Revision: D83964083

Pulled By: javache

fbshipit-source-id: 46dc074ca9b7fc97fa5a37ef48d68a895e3310ff