x11-wm/cosmic-comp: update to 1.0.0.b.6

Changes: https://github.com/pop-os/cosmic-comp/compare/epoch-1.0.0-beta.2...epoch-1.0.0-beta.6
Reported by: Repology

(cherry picked from commit ae35de605ad40f31eddfed0fdef27c33dabaaf9a)