Trying Jayme's solution seems to have worked in my case:
- Put host into maintenance mode
- Manually run "dnf update" on the host to update ovirt-node-ng-image-update to
4.5.5 from 4.5.4.
- Reboot host
- In Manager GUI, click "check for updates" once again on the updated node,
which should clear the notification that updates are available.