[3.7] bpo-33747: Avoid mutating the global sys.modules dict in unittest.mock...

[3.7] bpo-33747: Avoid mutating the global sys.modules dict in unittest.mock tests (GH-8520) (GH-11031)



(cherry picked from commit 3cf74384b53b998fa846dc2590cedf9ad2a0d5fd)


Co-authored-by: Anirudha Bose <ani07nov@gmail.com>


https://bugs.python.org/issue33747