gh-99728: correct typo in datetime format codes documentation (GH-99750)

(cherry picked from commit d5f8a2b)

Co-authored-by: Brad Wolfe <[email protected]>

Author: miss-islington

Doc/library/datetime.rst

@@ -2589,7 +2589,7 @@ Notes:
 
 (9)
    When used with the :meth:`strptime` method, the leading zero is optional
-   for  formats ``%d``, ``%m``, ``%H``, ``%I``, ``%M``, ``%S``, ``%J``, ``%U``,
+   for  formats ``%d``, ``%m``, ``%H``, ``%I``, ``%M``, ``%S``, ``%j``, ``%U``,
    ``%W``, and ``%V``. Format ``%y`` does require a leading zero.
 
 .. rubric:: Footnotes