refac: modernize type annotations (PEP 604 / PEP 585)

backend/open_webui/retrieval/vector/main.py

@@ -1,7 +1,8 @@
-from pydantic import BaseModel
 from abc import ABC, abstractmethod
 from typing import Any, Dict, List, Optional, Union
 
+from pydantic import BaseModel
+
 
 class VectorItem(BaseModel):
     id: str