The new added attribute `self.actual_file_to_check` is not one of template_fields and is initiated in `self.__init__()`. So, it need to be updated after `self.path` is rendered. Otherwise, the template in `self.path` will not work.

It is not necessary for `self.actual_file_to_check` to be an attribute. Deleted it from `__init__`. Replaced it with a local variable in `SFTPSensor.poker()`.