[3.13] gh-130160: use `.. program::` directive for documenting `doctest` CLI (GH-131034) (#131320)

gh-130160: use `.. program::` directive for documenting `doctest` CLI (GH-131034)
(cherry picked from commit 9558d22ac308c102e4f843541eead2022050225e)

Co-authored-by: donBarbos <donbarbos@proton.me>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>