[libc++] Fix incorrect REQUIRES on a locale-dependent test

The test doesn't depend specifically on the en_US.UTF-8 locale, instead
it depends on whether localization support exists, period.

Differential Revision: https://reviews.llvm.org/D114708

GitOrigin-RevId: a8278a747ddf9e56262dafddd7c03e29cd85d074
1 file changed