glib: Fix Windows build
With GCC ../glib/gspawn-win32.c:548:33: error: passing argument 2 of '_spawnve' from incompatible pointer type
And MSVC ../glib/gspawn-win32.c(548): warning C4133: 'function': incompatible types - from 'wchar_t *' to 'const char *'
Applying upstream MR https://gitlab.gnome.org/GNOME/glib/-/merge_requests/3237