screencast: Correct expected bus name for streams

Previously, this only worked because GDBusConnection was not filtering
signals by their sender correctly (GNOME/glib#3268).

Thanks: Alicia Boya García
Signed-off-by: Simon McVittie <smcv@debian.org>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3303>

js/dbusServices/screencast/screencastService.js

@@ -340,7 +340,7 @@ class Recorder extends Signals.EventEmitter {
                 });
 
             this._streamProxy = new ScreenCastStreamProxy(Gio.DBus.session,
-                'org.gnome.ScreenCast.Stream',
+                'org.gnome.Mutter.ScreenCast',
                 streamPath);
 
             this._streamProxy.connectSignal('PipeWireStreamAdded',