Update imports to match anyio docs

backend/open_webui/main.py

@@ -11,13 +11,13 @@ import random
 
 from contextlib import asynccontextmanager
 from urllib.parse import urlencode, parse_qs, urlparse
-from anyio import to_thread
 from pydantic import BaseModel
 from sqlalchemy import text
 
 from typing import Optional
 from aiocache import cached
 import aiohttp
+import anyio.to_thread
 import requests
 
 
@@ -439,7 +439,8 @@ async def lifespan(app: FastAPI):
 
     pool_size = THREAD_POOL_SIZE
     if pool_size and pool_size > 0:
-        to_thread.current_default_thread_limiter().total_tokens = pool_size
+        limiter = anyio.to_thread.current_default_thread_limiter()
+        limiter.total_tokens = pool_size
 
     asyncio.create_task(periodic_usage_pool_cleanup())
     yield