📝 Update source examples and docs from Python 3.9 to 3.10 (#14900)

docs_src/background_tasks/tutorial001_py310.py

@@ -0,0 +1,15 @@
+from fastapi import BackgroundTasks, FastAPI
+
+app = FastAPI()
+
+
+def write_notification(email: str, message=""):
+    with open("log.txt", mode="w") as email_file:
+        content = f"notification for {email}: {message}"
+        email_file.write(content)
+
+
+@app.post("/send-notification/{email}")
+async def send_notification(email: str, background_tasks: BackgroundTasks):
+    background_tasks.add_task(write_notification, email, message="some notification")
+    return {"message": "Notification sent in the background"}