The inclusion of Arc-KDE fixes T5993
Test Plan:
Arc-KDE theme present in KDE system config (desktop theme, color scheme, window decorator...)
Theme applied with success
Reviewers: Triage Team, sunnyflunk
Reviewed By: Triage Team, sunnyflunk
Subscribers: sunnyflunk
Maniphest Tasks: T5993
Differential Revision: https://dev.solus-project.com/D3577