Fix the syntax used in a831132

This library supports Python < 3.10

src/quart_auth/extension.py

@@ -2,7 +2,7 @@
 from contextlib import asynccontextmanager
 from enum import auto, Enum
 from hashlib import sha512
-from typing import Any, AsyncGenerator, cast, Dict, Optional
+from typing import Any, AsyncGenerator, cast, Dict, Optional, Union
 
 from itsdangerous import BadSignature, SignatureExpired, URLSafeTimedSerializer
 from quart import (
@@ -46,7 +46,7 @@ class Action(Enum):
 
 
 class _AuthSerializer(URLSafeTimedSerializer):
-    def __init__(self, secret: str | bytes, salt: str) -> None:
+    def __init__(self, secret: Union[str, bytes], salt: str) -> None:
         super().__init__(secret, salt, signer_kwargs={"digest_method": sha512})