pythongh-141510: Update PyDict_Copy documentation with note on frozendict (pythonGH-145249)

Author: eendebakpt

Doc/c-api/dict.rst

@@ -82,6 +82,9 @@ Dictionary objects
 
    Return a new dictionary that contains the same key-value pairs as *p*.
 
+   .. versionchanged:: next
+      If *p* is a subclass of :class:`frozendict`, the result will be a
+      :class:`frozendict` instance instead of a :class:`dict` instance.
 
 .. c:function:: int PyDict_SetItem(PyObject *p, PyObject *key, PyObject *val)