bpo-35250: Correct argument name "num" -> "btn" in turtle docs. (GH-10565)

(cherry picked from commit 4edeaeac4c194ba5d09187640b5cfca5e03be617)

Co-authored-by: Srinivas  Thatiparthy (శ్రీనివాస్  తాటిపర్తి) <thatiparthysreenivas@gmail.com>
diff --git a/Lib/turtle.py b/Lib/turtle.py
index 9db564b..47a94f2 100644
--- a/Lib/turtle.py
+++ b/Lib/turtle.py
@@ -1352,7 +1352,7 @@
         Arguments:
         fun -- a function with two arguments, the coordinates of the
                clicked point on the canvas.
-        num -- the number of the mouse-button, defaults to 1
+        btn -- the number of the mouse-button, defaults to 1
 
         Example (for a TurtleScreen instance named screen)
 
@@ -3526,7 +3526,7 @@
         Arguments:
         fun --  a function with two arguments, to which will be assigned
                 the coordinates of the clicked point on the canvas.
-        num --  number of the mouse-button defaults to 1 (left mouse button).
+        btn --  number of the mouse-button defaults to 1 (left mouse button).
         add --  True or False. If True, new binding will be added, otherwise
                 it will replace a former binding.
 
@@ -3547,7 +3547,7 @@
         Arguments:
         fun -- a function with two arguments, to which will be assigned
                 the coordinates of the clicked point on the canvas.
-        num --  number of the mouse-button defaults to 1 (left mouse button).
+        btn --  number of the mouse-button defaults to 1 (left mouse button).
 
         Example (for a MyTurtle instance named joe):
         >>> class MyTurtle(Turtle):
@@ -3572,7 +3572,7 @@
         Arguments:
         fun -- a function with two arguments, to which will be assigned
                the coordinates of the clicked point on the canvas.
-        num -- number of the mouse-button defaults to 1 (left mouse button).
+        btn -- number of the mouse-button defaults to 1 (left mouse button).
 
         Every sequence of mouse-move-events on a turtle is preceded by a
         mouse-click event on that turtle.