[Bug libstdc++/119517] formatter for chrono types are underconstrained

[tkaminsk at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119517

--- Comment #2 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
Jonathan noted that zoned_time is specified in standard to accept unconstrained
FormatContext in [time.format] p19 (https://eel.is/c++draft/time.format#19).