plugins/fadingpopups: don't block direct scanout
The effect only modifies the opacity of individual windows that WorkspaceScene::scanoutCandidate will reject anyways, so there's no reason for it to block direct scanout. Once a more proper solution for blocking direct scanout on individual items is in place, this can be removed again
(cherry picked from commit de8bd8f1)
Co-authored-by: Xaver Hugl xaver.hugl@gmail.com