pythongh-109700: fix memory error handling in PyDict_SetDefault (python#136338)

(cherry picked from commit d22e073)

Author: kumaraditya303

Misc/NEWS.d/next/Core and Builtins/2025-07-06-14-53-19.gh-issue-109700.KVNQQi.rst

@@ -0,0 +1 @@
+Fix memory error handling in :c:func:`PyDict_SetDefault`.

Objects/dictobject.c

@@ -4340,6 +4340,7 @@ dict_setdefault_ref_lock_held(PyObject *d, PyObject *key, PyObject *default_valu
             if (result) {
                 *result = NULL;
             }
+            return -1;
         }
 
         MAINTAIN_TRACKING(mp, key, value);