UT: Use new Publisher for each test instead of default `pub`

Using the default publisher provided by pypubsub causes state to be
carried over between tests. Unit tests should not depend on eachother or
the order in which they're run.

monkey/tests/unit_tests/common/event_queue/test_pypubsub_event_queue.py

@@ -4,7 +4,7 @@ from typing import FrozenSet, Union
 from uuid import UUID
 
 import pytest
-from pubsub import pub
+from pubsub.core import Publisher
 
 from common.event_queue.pypubsub_event_queue import PyPubSubEventQueue
 from common.events import AbstractEvent
@@ -49,7 +49,7 @@ def subscriber():
 
 @pytest.fixture
 def event_queue():
-    return PyPubSubEventQueue(pub)
+    return PyPubSubEventQueue(Publisher())
 
 
 def test_subscribe_all(event_queue, subscriber):