Notification icon shows available upgrades even if they are set to be installed automatically
This is to keep track of the situation described there: https://trisquel.info/en/forum/security-updates-are-not-getting-installed-automatically-trisquel-11-aramo.
If the options for security upgrades in "Software and updates" are to "Download and install automatically" daily, the notification icon may still be displayed in the notification area after the upgrades have been downloaded, letting the user believe that further action may be required on their part for the upgrades to be installed.
unattended-upgrade is running apt-update and apt-upgrade as two separate jobs, each with its own randomized timer, so maybe update-notifier should be turned off in that user case to avoid confusion.