Update dbus-advertised screencast source types

Resolve an issue where OBS Studio 27.1 does not make its
"Window Capture (PipeWire)" source active and usable under
the wayland version of Plasma. This new version of OBS queries
the AvailableSourceTypes dbus property to decide whether to load
either or both of its wayland screen capture modules (one for
a whole monitor, one for per-window capture).