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

(cherry picked from commit d41ec65ab7411e877ca33d05e8c900feca530635)

Co-authored-by: Zackery Spytz <zspytz@gmail.com>
diff --git a/Doc/tutorial/datastructures.rst b/Doc/tutorial/datastructures.rst
index ff4c797..5c6b65f 100644
--- a/Doc/tutorial/datastructures.rst
+++ b/Doc/tutorial/datastructures.rst
@@ -78,7 +78,7 @@
    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