Hi,
It doesn't have to be periodically - you can watch the rabbitmq-server releases on github (
https://github.com/rabbitmq/rabbitmq-server -> Watch -> Custom -> Releases) to be notified whenever a version is released. We also send announcement emails but this way you'll be notified immediately. Also works for other projects hosted on Github obviously.
For security-specific notifications, we have just started publishing advisories to the Github Security Advisory Database:
https://github.com/rabbitmq/rabbitmq-server/security/advisories. Unfortunately from what I can tell, Github doesn't send notifications about new advisories being published (at least when watched with Watch -> Custom -> Security Alerts) but perhaps there are other ways to stay up to date with these.
Best,