Sygnal healthcheck returns 200 when notification-sending is 500ing.

*This issue was originally created by [**@lampholder**](https://github.com/lampholder) at .*

I've received a report from a customer that Sygnal is failing to send notifications returning a 500, while its healthcheck on /health still returns 200, causing problems because no automatic kubernetes failover restart is being triggered.

They've pointed the finger at a faulty database connection pool : sygnal psycopg2.InterfaceError: connection already closed

They've provided logs, but I'll keep those off this issue for now - let me know if you want to review the logs to investigate,