FIX matplotlib#5680 span selector + blit + span_stays broken

The rect properties for the 'live' rect were being forwarded re-used
for the stay artist, however if blitting is used, then 'animated' is
set which exclude the artist from the normal draw tree.

lib/matplotlib/widgets.py

@@ -1473,6 +1473,7 @@ def new_axes(self, ax):
                                        transform=trans,
                                        visible=False,
                                        **self.rectprops)
+            self.stay_rect.set_animated(False)
             self.ax.add_patch(self.stay_rect)
 
         self.ax.add_patch(self.rect)