pythongh-83728: Add hmac.new default parameter deprecation (pythonGH-91939)

(cherry picked from commit 56b5daf)

Co-authored-by: Stanley <46876382+slateny@users.noreply.github.com>

Author: slateny

Doc/whatsnew/3.8.rst

@@ -2005,6 +2005,8 @@ Changes in the Python API
   ``replace()`` method of :class:`types.CodeType` can be used to make the code
   future-proof.
 
+* The parameter ``digestmod`` for :func:`hmac.new` no longer uses the MD5 digest
+  by default.
 
 Changes in the C API
 --------------------