[llvm] [libc++] Fix CODEOWNERS file for libc++ (PR #65344)

[Tom Stellard via llvm-commits]

tstellar wrote:

@ldionne I've updated https://github.com/llvm/llvm-project/pull/64913  I'll try to land that tomorrow and then we can set up the reviewer teams for libcxx and libcxxabi.

https://github.com/llvm/llvm-project/pull/65344