[3.13] gh-137273: Fix debug assertion failure in locale.setlocale() on Windows (GH-137300) (GH-137306)

It happened when there were at least 16 characters after dot in the
locale name.
(cherry picked from commit 718e0c89ba0610bba048245028ac133bbf2d44c2)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>