bpo-44679: [doc] fix typo in unittest.mock.rst (GH-27618) (GH-27619)

(cherry picked from commit 938e84b)

Co-authored-by: Jack DeVries <58614260+jdevries3133@users.noreply.github.com>

Author: miss-islington

Doc/library/unittest.mock.rst

@@ -2207,7 +2207,7 @@ In this example we monkey patch ``method`` to return ``sentinel.some_object``:
     >>> real.method.return_value = sentinel.some_object
     >>> result = real.method()
     >>> assert result is sentinel.some_object
-    >>> sentinel.some_object
+    >>> result
     sentinel.some_object