Build fix for ambiguity with gcc >= 14

[agmt]

Resolves building with gcc-14 (-std=c++20):

In attempt to build:

#include <sstream>
#include <chrono>
#include <date/date.h>

int main() {
    std::istringstream Stream("2023-10-05 14:30:00");
    std::chrono::system_clock::time_point TimePoint;
    Stream >> date::parse("%F %T", TimePoint);
}

compiler reports a conflict of date/date.h with c++/14/bits/chrono_io.h:

date/include/date/date.h:8290:28: error: call of overloaded ‘from_stream(std::basic_istream<char>&, const char*&, std::chrono::time_point<std::chrono::_V2::system_clock, std::chrono::duration<long int, std::ratio<1, 1000000000> > >&)’ is ambiguous
 8290 |     -> decltype(from_stream(std::declval<std::basic_istream<CharT>&>(), format, tp),
      |                 ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

date/include/date/date.h:8025:1: note: candidate: ‘std::basic_istream<_CharT, _Traits>& date::from_stream(std::basic_istream<_CharT, _Traits>&, const CharT*, sys_time<Duration>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>*, std::chrono::minutes*) [with Duration = std::chrono::duration<long int, std::ratio<1, 1000000000> >; CharT = char; Traits = std::char_traits<char>; Alloc = std::allocator<char>; sys_time<Duration> = std::chrono::time_point<std::chrono::_V2::system_clock, std::chrono::duration<long int, std::ratio<1, 1000000000> > >; std::chrono::minutes = std::chrono::duration<long int, std::ratio<60> >]’
 8025 | from_stream(std::basic_istream<CharT, Traits>& is, const CharT* fmt,

/usr/include/c++/14/bits/chrono_io.h:2750:5: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::chrono::from_stream(std::basic_istream<_CharT, _Traits>&, const _CharT*, sys_time<_Duration>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>*, minutes*) [with _CharT = char; _Traits = std::char_traits<char>; _Duration = duration<long int, std::ratio<1, 1000000000> >; _Alloc = std::allocator<char>; sys_time<_Duration> = time_point<_V2::system_clock, duration<long int, std::ratio<1, 1000000000> > >; minutes = duration<long int, std::ratio<60> >]’
 2750 |     from_stream(basic_istream<_CharT, _Traits>& __is, const _CharT* __fmt,
      |     ^~~~~~~~~~~

The issue has been introduced at f079e35
The patch is working on g++-11 and g++-14

[HowardHinnant]

I encourage clients to use <chrono> in place of this library on this platform.