[3.13] gh-125254: Fix error report about ambiguous option in argparse (GH-125273) (GH-125359)

This was a regression introduced in gh-58573. It was only tested for the
case when the ambiguous option is the last argument in the command line.
(cherry picked from commit 63cf4e914f879ee28a75c02e867baa7c6047ea2b)

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