fix: correct Self import

Author: Félix Rohrlich

scim2_models/messages/bulk.py

@@ -1,12 +1,12 @@
 from enum import Enum
 from typing import Annotated
 from typing import Any
-from typing import Self
 
 from pydantic import Field
 from pydantic import PlainSerializer
 from pydantic import ValidationInfo
 from pydantic import model_validator
+from typing_extensions import Self
 
 from ..annotations import Required
 from ..annotations import Returned