[SystemTray] Fix model update in settings (missing icon)

Summary:
Fixes a bug, when system tray settings is opened and new application is opened, view is not correctly refreshed and icon is missing. Caused by duplicated role names. Related to: D26586

BUG: 416400
FIXED-IN: 5.18.0

Test Plan:
1. Open system tray settings
2. Open an app with systray icon
Expected:
Icon, title etc are correctly rendered.

Reviewers: #plasma_workspaces, #plasma, davidedmundson, ngraham, broulik

Reviewed By: #plasma_workspaces, #plasma, davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D26850