Supress some protected-access warnings when django-simple-history is installed.

[m000]

django-simple-hisory is a fairly popular [1] package for keeping track of changes in django objects. Setting the _change_reason property of an object is the officially documented way to provide a value for the history_change_reason field of historical objects [2].

When django-simple-hisory is installed, protected-access warnings for setting _change_reason is most likely a false positive, and should be supressed.

Because of inherent limitations of pylint, this may lead to some false negatives if _change_reason is used elsewhere.

[1] https://pypistats.org/packages/django-simple-history [2] https://django-simple-history.readthedocs.io/en/latest/historical_model.html#change-reason