fix doc strings

Author: s-light

adafruit_displayio_layout/widgets/cartesian.py

@@ -612,6 +612,7 @@ def add_line(self, x: int, y: int) -> None:
         :param int x: ``x`` coordinate in the local plane
         :param int y: ``y`` coordinate in the local plane
         :return: None
+
         rtype: None
         """
         self._add_point(x, y)
@@ -633,6 +634,7 @@ def clear_lines(self, palette_index=5):
 
         :param int palette_index: color palett index. Defaults to 5
         :return: None
+
         rtype: None
         """
         self.plot_line_point = None