Update HasFault

Author: JordonPhillips

packages/smithy-core/src/smithy_core/interfaces/exceptions.py

@@ -1,6 +1,8 @@
 #  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 #  SPDX-License-Identifier: Apache-2.0
-from typing import ClassVar, Literal, Protocol, runtime_checkable
+from typing import Protocol, runtime_checkable
+
+from ..exceptions import Fault
 
 
 @runtime_checkable
@@ -10,4 +12,4 @@ class HasFault(Protocol):
     All modeled errors will have a fault that is either "client" or "server".
     """
 
-    fault: ClassVar[Literal["client", "server"]]
+    fault: Fault | None