pythongh-107755: Document the correct default value of slice step (pythonGH-107756)

Document the correct default value of slice step.
(cherry picked from commit 9bf350b)

Co-authored-by: wim glenn <hey@wimglenn.com>

Author: wimglenn

Doc/library/functions.rst

@@ -1630,7 +1630,7 @@ are always available.  They are listed here in alphabetical order.
 
 
 .. class:: slice(stop)
-           slice(start, stop, step=1)
+           slice(start, stop, step=None)
 
    Return a :term:`slice` object representing the set of indices specified by
    ``range(start, stop, step)``.  The *start* and *step* arguments default to