📝 Fix async test example not to trigger DeprecationWarning (#12084)

docs_src/async_tests/test_main.py

@@ -1,12 +1,14 @@
 import pytest
-from httpx import AsyncClient
+from httpx import ASGITransport, AsyncClient
 
 from .main import app
 
 
 @pytest.mark.anyio
 async def test_root():
-    async with AsyncClient(app=app, base_url="http://test") as ac:
+    async with AsyncClient(
+        transport=ASGITransport(app=app), base_url="http://test"
+    ) as ac:
         response = await ac.get("/")
     assert response.status_code == 200
     assert response.json() == {"message": "Tomato"}