bpo-44968: Fix test_subprocess_wait_no_same_group in test_asyncio (GH-27870)

The code of the test was never executed because the test function
was unintentionally converted to a generator function.
(cherry picked from commit 585390fdd8661b4bc08bdfc27551292da9b4b9b8)

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