Update the vendored copy of libexpat to 2.4.1 (from 2.2.8) to get the
fix for the CVE-2013-0340 "Billion Laughs" vulnerability. This copy
is most used on Windows and macOS.
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
(cherry picked from commit 3fc5d84046)
Co-authored-by: Victor Stinner <vstinner@python.org>