Add icon to notifyrc back

This was removed to drop the notificationsplugin's "No icon" hack, but de facto all notifications have icons.

This makes sure that the KDE Connect entry in the notifications KCM has an icon
1 job for master in 6 minutes and 26 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #47470
linux kf5-qt5 qt5.12

00:06:26

17.0%