Fixes:
../kwin/mobiletaskswitcher/plugin/taskfiltermodel.cpp:81:40: error: ‘class KWin::Workspace’ has no member named ‘activities’; did you mean ‘ActivityRaise’?
81 | auto activity = Workspace::self()->activities()->current();
| ^~~~~~~~~~
| ActivityRaise
This occurs when KWin is built with -DKWIN_BUILD_ACTIVITIES=OFF:
https://invent.kde.org/plasma/kwin/-/blob/master/src/workspace.h#L424