[3.12] gh-110378: Fix test_async_gen_propagates_generator_exit in test_contextlib_async (GH-110500) (#110610)

It now fails if the original bug is not fixed, and no longer produce ResourceWarning with fixed code.
(cherry picked from commit 5aa62a8de15212577a13966710b3aede46e93824)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>