bpo-46436: Fix command-line option -d/--directory in module http.server (GH-30701)

Fix command-line option -d/--directory in http.server main
function that was ignored when combined with --cgi.

Automerge-Triggered-By: GH:merwok
(cherry picked from commit 2d080347d74078a55c47715d232d1ab8dc8cd603)

Co-authored-by: Géry Ogam <gery.ogam@gmail.com>

Co-authored-by: Géry Ogam <gery.ogam@gmail.com>