[3.13] gh-124969: Make locale.nl_langinfo(locale.ALT_DIGITS) returning a string again (GH-125774) (GH-125804)

This is a follow up of GH-124974. Only Glibc needed a fix.
Now the returned value is a string consisting of semicolon-separated
symbols on all Posix platforms.
(cherry picked from commit dcc4fb2c9068f60353f0c0978948b7681f7745e6)

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