[3.13] gh-129401: Test repr rlock failing randomly (GH-129959) (#144405)

Fix and simplify a test of `test_repr_rlock` about multiprocessing.RLock primitive.
(cherry picked from commit a98a6bd1128663fbe58c0c73d468710245a57ad6)

Co-authored-by: Duprat <yduprat@gmail.com>