test: fix a race condition in the controller unit tests (aws-deadline#1031)

Signed-off-by: Justin Sawatzky <132946620+justinsaws@users.noreply.github.com>

Author: justinsaws

test/unit/deadline_client/ui/controllers/test_deadline_controller.py

@@ -153,6 +153,7 @@ def test_refresh_farms_handles_error(self, mock_api, qtbot):
         controller.refresh_farms()
 
         qtbot.waitUntil(lambda: len(farms_received) > 0, timeout=2000)
+        qtbot.waitUntil(lambda: len(errors_received) > 0, timeout=2000)
 
         # Should emit empty list on error
         assert farms_received[0] == []