[3.9] bpo-43517 (followup): Install additional test directory (GH-24950) by pitrou · Pull Request #24951 · python/cpython

…GH-24950)

Should fix some CI failures on buildbots that test an installed version of Python.

Automerge-Triggered-By: GH:pitrou
(cherry picked from commit 66c8adf)

Co-authored-by: Antoine Pitrou <antoine@python.org>