gh-83728: Add hmac.new default parameter deprecation (GH-91939)

Doc/whatsnew/3.8.rst

@@ -2008,6 +2008,8 @@ 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
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