code: def _last_of_quarter(self, day_of_week=None):
          
          return self.set(self.year, self.quarter * 3, 1).last_of("month", day_of_week)
docs: Modify to the last occurrence of a given day of the week
          in the current quarter. If no day_of_week is provided,
          modify to the last day of the quarter. Use the supplied consts
          to indicate the desired day_of_week, ex. pendulum.MONDAY.
  
          :type day_of_week: int or None
  
          :rtype: Date