Show a notification when just one firmware is installed

This means we show the same UI if the user installs all the firmware updates or
just one of them. We don't want the user to think the update was done live.
1 job for <span class="ref-name">wip/hughsie/notify-firmware-requires-update</span> in 18 minutes and 57 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #305760
build-gnome-software

00:18:57