Cleanup test environment and requirements

- pytest: verbose isn't needed but show skipped tests
- mock is not needed anymore. it is part of stdlib
- Unpin Sphinx and fix warning about lexer
- Mirror tox command for doc build in tasks.py

pelican/tests/test_rstdirectives.py

@@ -1,15 +1,8 @@
+from unittest.mock import Mock
+
 from pelican.tests.support import unittest
 
-try:
-    from unittest.mock import Mock
-except ImportError:
-    try:
-        from mock import Mock
-    except ImportError:
-        Mock = False
 
-
-@unittest.skipUnless(Mock, 'Needs Mock module')
 class Test_abbr_role(unittest.TestCase):
     def call_it(self, text):
         from pelican.rstdirectives import abbr_role