[stable-2.13] Use unittest.mock instead of mock. (#77883)

This can only be done for controller tests.
(cherry picked from commit 3a9a23fb1a)

Co-authored-by: Matt Clay <matt@mystile.com>

test/units/executor/test_task_queue_manager_callbacks.py

@@ -19,7 +19,7 @@
 from __future__ import (absolute_import, division, print_function)
 
 from units.compat import unittest
-from mock import MagicMock
+from unittest.mock import MagicMock
 
 from ansible.executor.task_queue_manager import TaskQueueManager
 from ansible.playbook import Playbook