* gh-108388: Convert test_concurrent_futures to package (#108401)
Convert test_concurrent_futures to a package of sub-tests.
(cherry picked from commit aa6f787faa)
Notes on backport to 3.11:
* AsCompletedTests: Revert test_future_times_out() => test_zero_timeout()
* Restore TODO comment
* ThreadPoolExecutorTest.test_hang_global_shutdown_lock():
add @support.requires_resource('cpu').
Victor Stinner