[Clang] Never consider conversion from single-element braced-init-list perfect (#138307)
We might prefer a template std::initializer list constructor.
Fix a regression introduced by #136203
https://github.com/llvm/llvm-project/pull/136203#issuecomment-2843498895
GCC had a similar issue and a similar fix
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100963