pythongh-67230: document new csv quoting modes in whatsnew (pythongh-103491)

Author: smontanaro

Doc/whatsnew/3.12.rst

@@ -253,6 +253,13 @@ asyncio
 * :func:`asyncio.wait` now accepts generators yielding tasks.
   (Contributed by Kumar Aditya in :gh:`78530`.)
 
+csv
+---
+
+* Add :data:`~csv.QUOTE_NOTNULL` and :data:`~csv.QUOTE_STRINGS` flags to
+  provide finer grained control of ``None`` and empty strings by
+  :class:`~csv.reader` and :class:`~csv.writer` objects.
+
 inspect
 -------