[3.13] gh-124402: Require cpu resource in test_super slow method (GH-124434) (#124468)

gh-124402: Require cpu resource in test_super slow method (GH-124434)

test___class___modification_multithreaded() now requires the 'cpu'
test resource on a Free Threaded build.
(cherry picked from commit 5a605660745d32a9b9f4208666889c702527208c)

Co-authored-by: Victor Stinner <vstinner@python.org>