Fix changelog argument name

Co-authored-by: Elliott Sales de Andrade <[email protected]>

Author: dstansby

doc/users/next_whats_new/polygon_selector_box.rst

@@ -1,6 +1,6 @@
 PolygonSelector bounding boxes
 ------------------------------
-`~matplotlib.widgets.PolygonSelector` now has a *draw_box* argument, which
+`~matplotlib.widgets.PolygonSelector` now has a *draw_bounding_box* argument, which
 when set to `True` will draw a bounding box around the polygon once it is
 complete. The bounding box can be resized and moved, allowing the points of
 the polygon to be easily resized.