Fix standalone mock support (#531)

It was removed by accident in #528 after running `pyupgrade --py39-plus`.

Fix #530

Author: nicoddemus

src/pytest_mock/_util.py

@@ -15,7 +15,7 @@ def get_mock_module(config):
             config.getini("mock_use_standalone_module")
         )
         if use_standalone_module:
-            from unittest import mock
+            import mock
 
             _mock_module = mock
         else:

tox.ini

@@ -5,6 +5,8 @@ envlist = py{39,310,311,312,313,314}, norewrite, pytest6
 [testenv]
 deps =
     coverage
+    # Used for standalone mock support.
+    mock
     pytest-asyncio
     pytest6: pytest==6.2.5
 commands =