[3.12] gh-85453: Consistent backquotes on None occurences across datetime.rst (GH-118282) (#118419)

(cherry picked from commit 0f79740)

Co-authored-by: edson duarte <[email protected]>

Author: miss-islington

Doc/library/datetime.rst

@@ -1691,7 +1691,7 @@ day, and subject to adjustment via a :class:`tzinfo` object.
    * ``fold in [0, 1]``.
 
    If an argument outside those ranges is given, :exc:`ValueError` is raised. All
-   default to 0 except *tzinfo*, which defaults to :const:`None`.
+   default to 0 except *tzinfo*, which defaults to ``None``.
 
 Class attributes: