bpo-42489: Fix the signature for list.sort() in the tutorial (GH-23538)

(cherry picked from commit d41ec65a)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>

Doc/tutorial/datastructures.rst

@@ -78,7 +78,7 @@ objects:
    Return the number of times *x* appears in the list.
 
 
-.. method:: list.sort(key=None, reverse=False)
+.. method:: list.sort(*, key=None, reverse=False)
    :noindex:
 
    Sort the items of the list in place (the arguments can be used for sort