[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/plugins/test_plugins.py

@@ -23,7 +23,7 @@ __metaclass__ = type
 import os
 
 from units.compat import unittest
-from mock import patch, MagicMock
+from unittest.mock import patch, MagicMock
 from ansible.plugins.loader import PluginLoader, PluginPathContext