[Bug libstdc++/93244] std::filesystem::path::generic_string doesn't convert the first slash on Windows

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93244

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Doh, copy&paste error from the previous commit.

That belongs to PR 94069.