[3.12] gh-81691: Fix handling of multiple "--" (double dashes) in argparse (GH-124233) (GH-124267)

Only the first one has now been removed, all subsequent ones are now
taken literally.
(cherry picked from commit aae126748ff3d442fdbcd07933855ffd7ae6f59c)

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