[3.12] gh-67230: Add versionadded notes for QUOTE_NOTNULL and QUOTE_STRINGS (GH-114816) (#114840)

As @GPHemsley pointed out, GH-29469 omitted `versionadded` notes for the 2 new items.
(cherry picked from commit 586057e)

Co-authored-by: Skip Montanaro <[email protected]>

Author: miss-islington

Doc/library/csv.rst

@@ -351,6 +351,8 @@ The :mod:`csv` module defines the following constants:
    Instructs :class:`reader` objects to interpret an empty (unquoted) field as None and
    to otherwise behave as :data:`QUOTE_ALL`.
 
+   .. versionadded:: 3.12
+
 .. data:: QUOTE_STRINGS
 
    Instructs :class:`writer` objects to always place quotes around fields
@@ -360,6 +362,8 @@ The :mod:`csv` module defines the following constants:
    Instructs :class:`reader` objects to interpret an empty (unquoted) string as ``None`` and
    to otherwise behave as :data:`QUOTE_NONNUMERIC`.
 
+   .. versionadded:: 3.12
+
 The :mod:`csv` module defines the following exception: