bpo-41819: Fix compiler warning in init_dump_ascii_wstr() (GH-22332)


Fix the compiler warning:

format specifies type `wint_t` (aka `int`) but the argument has type `unsigned int`
(cherry picked from commit c322948892438a387d752ec18d1eb512699a4d67)

Co-authored-by: Samuel Marks <807580+SamuelMarks@users.noreply.github.com>