Update Docs - FastAPI on_startup method to lifespan

Author: Yuerchu

docs/tutorial/fastapi/simple-hero-api.md

@@ -64,7 +64,7 @@ We want to make sure that once the app starts running, the function `create_tabl
 
 This should be called only once at startup, not before every request, so we put it in the function to handle the `"startup"` event:
 
-{* ./docs_src/tutorial/fastapi/simple_hero_api/tutorial001_py310.py ln[23:28] hl[26:28] *}
+{* ./docs_src/tutorial/fastapi/simple_hero_api/tutorial001_py310.py ln[24:30] hl[27:30] *}
 
 ## Create Heroes *Path Operation*
 

docs_src/tutorial/fastapi/simple_hero_api/tutorial001_py310.py

@@ -1,5 +1,6 @@
 from fastapi import FastAPI
 from sqlmodel import Field, Session, SQLModel, create_engine, select
+from contextlib import asynccontextmanager
 
 
 class Hero(SQLModel, table=True):
@@ -20,12 +21,13 @@ def create_db_and_tables():
     SQLModel.metadata.create_all(engine)
 
 
-app = FastAPI()
+app = FastAPI(lifespan=lifespan)
 
 
-@app.on_event("startup")
-def on_startup():
+@asynccontextmanager
+async def lifespan(app: FastAPI):
     create_db_and_tables()
+    yield
 
 
 @app.post("/heroes/")