fix: reduce latency of AsyncResult.get under gevent (celery#7052)

Wakeup waiters in `wait_for` after every `drain_events` occurs instead of only after 1 seconds timeout.

Does not block event loop, because `drain_events` of asynchronous backends with pubsub commonly sleeping for some nonzero time while waiting events.

t/unit/backends/test_asynchronous.py

@@ -158,7 +158,10 @@ def sleep(self):
 
     def result_consumer_drain_events(self, timeout=None):
         import eventlet
-        eventlet.sleep(0)
+        # `drain_events` of asynchronous backends with pubsub have to sleep
+        # while waiting events for not more then `interval` timeout,
+        # but events may coming sooner
+        eventlet.sleep(timeout/10)
 
     def schedule_thread(self, thread):
         import eventlet
@@ -204,7 +207,10 @@ def sleep(self):
 
     def result_consumer_drain_events(self, timeout=None):
         import gevent
-        gevent.sleep(0)
+        # `drain_events` of asynchronous backends with pubsub have to sleep
+        # while waiting events for not more then `interval` timeout,
+        # but events may coming sooner
+        gevent.sleep(timeout/10)
 
     def schedule_thread(self, thread):
         import gevent