fix: stop-the-world in type_set_qualname

Author: KowalskiThomas

Objects/typeobject.c

@@ -1594,7 +1594,12 @@ type_set_qualname(PyObject *tp, PyObject *value, void *context)
     }
 
     et = (PyHeapTypeObject*)type;
-    Py_SETREF(et->ht_qualname, Py_NewRef(value));
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    _PyEval_StopTheWorld(interp);
+    PyObject *old_qualname = et->ht_qualname;
+    et->ht_qualname = Py_NewRef(value);
+    _PyEval_StartTheWorld(interp);
+    Py_DECREF(old_qualname);
     return 0;
 }