[aurorae] Fix visibility of Context Help button
Summary:
providesContextHelp is a property of DecoratedClient, not Decoration.
BUG: 413145
FIXED-IN: 5.17.1
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Subscribers: kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D24851