[3.14] gh-109700: fix memory error handling in PyDict_SetDefault (GH-136338) (#136340)

gh-109700: fix memory error handling in `PyDict_SetDefault` (GH-136338)
(cherry picked from commit d22e073)

Co-authored-by: Kumar Aditya <[email protected]>

Author: miss-islington

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

@@ -4411,6 +4411,7 @@ dict_setdefault_ref_lock_held(PyObject *d, PyObject *key, PyObject *default_valu
             if (result) {
                 *result = NULL;
             }
+            return -1;
         }
 
         STORE_USED(mp, mp->ma_used + 1);