bpo-26952: [argparse] clearer error when formatting an empty mutually… (GH-30099) (GH-30114)

(cherry picked from commit 86de99588db3beff964137f4fe27dd1077a09b35)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
3 files changed