[Bug libstdc++/102280] span's range deduction guide is missing ranges::contiguous_range constraint

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102280

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I.e. please don't mark it as resolved, I'll do that when it's resolved.