[3.12] gh-116296: Fix refleak in reduce_newobj() corner case (GH-116297) (#116299)

(cherry picked from commit 17c4849)

Co-authored-by: Erlend E. Aasland <[email protected]>
Co-authored-by: Brandt Bucher <[email protected]>

Author: 3 people

Misc/NEWS.d/next/Core and Builtins/2024-03-04-10-19-51.gh-issue-116296.gvtxyU.rst

@@ -0,0 +1 @@
+Fix possible refleak in :meth:`!object.__reduce__` internal error handling.

Objects/typeobject.c

@@ -6258,6 +6258,7 @@ reduce_newobj(PyObject *obj)
     }
     else {
         /* args == NULL */
+        Py_DECREF(copyreg);
         Py_DECREF(kwargs);
         PyErr_BadInternalCall();
         return NULL;