[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/cache/test_cache.py

@@ -23,7 +23,7 @@ import os
 import shutil
 import tempfile
 
-import mock
+from unittest import mock
 
 from units.compat import unittest
 from ansible.errors import AnsibleError