Fix assertion in clone_combined_dict_keys()

Author: vstinner

Objects/dictobject.c

@@ -968,7 +968,9 @@ clone_combined_dict_keys(PyDictObject *orig)
     assert(orig->ma_keys != Py_EMPTY_KEYS);
     assert(orig->ma_keys->dk_refcnt == 1);
 
-    ASSERT_DICT_LOCKED(orig);
+    if (!PyFrozenDict_Check(orig)) {
+        ASSERT_DICT_LOCKED(orig);
+    }
 
     size_t keys_size = _PyDict_KeysSize(orig->ma_keys);
     PyDictKeysObject *keys = PyMem_Malloc(keys_size);