[build] Fix building with torch nightly (#27398)

It was blocking ort build with torch-nightly

Author: titaiwangms

tools/python/util/pytorch_export_helpers.py

@@ -1,6 +1,8 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License.
 
+from __future__ import annotations
+
 import inspect
 from collections import abc