[Bug c++/108195] [13 Regression] Incorrect implicit conversion when assigning initializer_list to std::vector

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108195

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Interesting the code works correctly for C++20 mode ...

Actually I made S's constructor constexpr and it made it work and not because
of C++20 mode.