bpo-32692: Fix test_threading.test_set_and_clear() (GH-8331)

Increase the timeout: give timeout x 4 instead of timeout x 2 to
threads to wait until the Event is set, but reduce the sleep from 500
ms to 250 ms. So the test should be more reliable and faster!
(cherry picked from commit 81950495)
Co-authored-by: Victor Stinner <vstinner@redhat.com>

Lib/test/lock_tests.py

@@ -405,12 +405,13 @@ class EventTests(BaseTestCase):
         # cleared before the waiting thread is woken up.
         evt = self.eventtype()
         results = []
+        timeout = 0.250
         N = 5
         def f():
-            results.append(evt.wait(1))
+            results.append(evt.wait(timeout * 4))
         b = Bunch(f, N)
         b.wait_for_started()
-        time.sleep(0.5)
+        time.sleep(timeout)
         evt.set()
         evt.clear()
         b.wait_for_finished()