[libcxx-commits] [libcxx] [libc++][mdspan][test] Correct `mapping::operator()` constraint tests (PR #201061)

[A. Jiang via libcxx-commits]

https://github.com/frederick-vs-ja approved this pull request.

LGTM. Some weird index types can render the `noexcept` not satisfied (as even though the `operator()` is `noexcept`, conversion to the parameter types can be potentially-throwing). But IMO we can improve the `noexcept` status later.

https://github.com/llvm/llvm-project/pull/201061