org.freedesktop.PowerManagement.Inhibit should only prevent suspend

For preventing screen standby or screen locking the org.freedesktop.ScreenSaver.Inhibit must be used.
Both calls erroneously did the same.

CHANGELOG: org.freedesktop.PowerManagement.Inhibit will only inhibit suspending the machine now (as per spec), to prevent screen power management use org.freedesktop.ScreenSaver.Inhibit instead

Differential Revision: https://phabricator.kde.org/D11182