RHEL9 Support - Test cases to leverage unittest.mock when possible (#658)

test/test_plugin_custom_xml.py

@@ -25,7 +25,14 @@
 import os
 import sys
 import re
-import mock
+try:
+    # Python 3.x
+    from unittest import mock
+
+except ImportError:
+    # Python 2.7
+    import mock
+
 import requests
 from apprise import plugins
 from apprise import Apprise