PYTHON-4021 Fix previous topologyDescription published when closing a client

[ShaneHarvey]

Small fix for PYTHON-4021 which resolves this test failure:

self = <test.test_discovery_and_monitoring.TestUnifiedReplicasetEmitTopologyChangedBeforeClose testMethod=test_Topology_lifecycle>

    def test_case(self):
>       self.run_scenario(spec)

test/unified_format.py:1953: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
test/unified_format.py:1897: in run_scenario
    self._run_scenario(spec, uri)
test/unified_format.py:1936: in _run_scenario
    self.check_events(expect_events)
test/unified_format.py:1801: in check_events
    self.match_evaluator.match_event(expected_event, actual_events[idx])
test/unified_format.py:940: in match_event
    self.match_event_fields(actual, spec)
test/unified_format.py:881: in match_event_fields
    self.match_topology_description(
test/unified_format.py:846: in match_topology_description
    self.test.assertEqual(getattr(actual, field), expected)
E   AssertionError: 'ReplicaSetNoPrimary' != 'ReplicaSetWithPrimary'
E   - ReplicaSetNoPrimary
E   ?           ^^
E   + ReplicaSetWithPrimary
E   ?           ^^^^