FastAPI: on_event() is deprecated, use lifespan event handlers instead.

[TheLovinator1]

    # TODO(TheLovinator): on_event() is deprecated, use lifespan event handlers instead.

https://github.com/TheLovinator1/discord-rss-bot/blob/ea3d7153d15192768c41f793086037ccc28a98b5/discord_rss_bot/main.py#L737