Issue #11790: Fix sporadic failures in test_multiprocessing.WithProcessesTestCondition.

Lib/test/test_multiprocessing.py

@@ -769,7 +769,13 @@ class _TestCondition(BaseTestCase):
         cond.release()
 
         # check they have all woken
-        time.sleep(DELTA)
+        for i in range(10):
+            try:
+                if get_value(woken) == 6:
+                    break
+            except NotImplementedError:
+                break
+            time.sleep(DELTA)
         self.assertReturnsIfImplemented(6, get_value, woken)
 
         # check state is not mucked up