make _MinimalArtist.get_figure consistent with Artist.get_figure

Co-authored-by: Thomas A Caswell <tcaswell@gmail.com>

Author: rcomer

lib/matplotlib/axes/_base.py

@@ -4754,7 +4754,10 @@ def __init__(self, figure, artists):
             self.artists = artists
 
         def get_figure(self, root=False):
-            return self.figure
+            if root:
+                return self.figure.get_figure(root=True)
+            else:
+                return self.figure
 
         @martist.allow_rasterization
         def draw(self, renderer):