pythongh-130106: Fix a typo in unittest.mock doc (pythonGH-130107)

(cherry picked from commit d2e60d8)

Co-authored-by: Srinivas Reddy Thatiparthy (తాటిపర్తి శ్రీనివాస్  రెడ్డి) <thatiparthysreenivas@gmail.com>

Doc/library/unittest.mock.rst

@@ -1984,7 +1984,7 @@ Imagine we have a project that we want to test with the following structure::
 
 Now we want to test ``some_function`` but we want to mock out ``SomeClass`` using
 :func:`patch`. The problem is that when we import module b, which we will have to
-do then it imports ``SomeClass`` from module a. If we use :func:`patch` to mock out
+do when it imports ``SomeClass`` from module a. If we use :func:`patch` to mock out
 ``a.SomeClass`` then it will have no effect on our test; module b already has a
 reference to the *real* ``SomeClass`` and it looks like our patching had no
 effect.