[3.12] gh-105699: Re-enable the Multiple-Interpreters Stress Tests (gh-107572) (#107783)

We had disabled them due to crashes they exposed, which have since been fixed.
(cherry picked from commit f9e3ff1ea4b2c8b787360409d55f2037652b7456)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
Co-authored-by: T. Wouters <thomas@python.org>