bpo-41720: Add "return NotImplemented" in turtle.Vec2D.__rmul__(). (GH-22092)

(cherry picked from commit fd4cafd4700dc03cb05fc2e5263c2666d785d6e3)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/turtle.py b/Lib/turtle.py
index ee67a35..ba8288d 100644
--- a/Lib/turtle.py
+++ b/Lib/turtle.py
@@ -258,6 +258,7 @@
     def __rmul__(self, other):
         if isinstance(other, int) or isinstance(other, float):
             return Vec2D(self[0]*other, self[1]*other)
+        return NotImplemented
     def __sub__(self, other):
         return Vec2D(self[0]-other[0], self[1]-other[1])
     def __neg__(self):