[3.13] gh-62480: De-personalize "Partial mocking" section in `unittest.mock` examples (GH-141321) (#141327)

gh-62480: De-personalize "Partial mocking" section in `unittest.mock` examples (GH-141321)

* Refine some wording in unittest partial mock doc

Some of the descriptions were addressed in first person,
but have now been changed to address the user reading the documentation instead.
(cherry picked from commit b618731781c31d4b5b75d199dfc14993ffd66e37)

Co-authored-by: KarnbirKhera <166065758+KarnbirKhera@users.noreply.github.com>
Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>