The documentation includes the URL that can be configured for checking for updates to the vyos images in two places.
The URLs in the 2 docs locations are different, and for the rolling release neither work anymore.
https://docs.vyos.io/en/rolling/installation/update.html
https://docs.vyos.io/en/rolling/configuration/system/updates.html

I propose these are both changed to the below URL:
https://raw.githubusercontent.com/vyos/vyos-rolling-nightly-builds/rolling/version.json