[Bug libstdc++/93884] ranges::copy doesn't like output iterators

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93884

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Looks like we do not yet implement parts of P0896R4 that make
back_insert_iterator and front_insert_iterator into valid C++20
output_iterators.