libstdc++: Fix brainwrong in path::_S_convert(T) [PR102743]

libstdc++: Fix brainwrong in path::_S_convert(T) [PR102743]

This function was supposed to check whether the parameter's value type
is the same as path::value_type, and therefore needs no conversion.
Instead it checks whether the parameter is the same as its own value
type, which is never true. This means we incorrectly return a string
view for the case where T is path::string_type, instead of just
returning the string itself. The only place that happens is
path::_S_convert_loc for Windows, where we call _S_convert with a
std::wstring rvalue.

This fixes the condition in _S_convert(T).

libstdc++-v3/ChangeLog:

	PR libstdc++/102743
	* include/bits/fs_path.h (path::_S_convert(T)): Fix condition
	for returning the same string unchanged.