gh-110383: Update dict get, fromkeys, and setdefault signatures in docs

Doc/library/stdtypes.rst

@@ -4575,7 +4575,7 @@ can be used interchangeably to index the same dictionary entry.
       such as an empty list.  To get distinct values, use a :ref:`dict
       comprehension <dict>` instead.
 
-   .. method:: get(key[, default])
+   .. method:: get(key[, default=None])
 
       Return the value for *key* if *key* is in the dictionary, else *default*.
       If *default* is not given, it defaults to ``None``, so that this method