[3.13] gh-123780: Make test_pkgutil clean up `spam` module (GH-123036) (#123781)

gh-123780: Make test_pkgutil clean up `spam` module (GH-123036)
(cherry picked from commit eca3fe40c251d51964172dd4e6e9c7d0d85d7d4a)

Co-authored-by: Malcolm Smith <smith@chaquo.com>