Mute all audio on right-click (#6708)

Previously, right-clicking the audio icon muted only the output. Whereas
the switch at the top of the panel mutes all audio (inputs and outputs).

Pairing the right-click to the switch seems a bit less confusing, and
also matches the behaviour with other panels (e.g. Bluetooth, Tailscale,
etc).

shell/plugins/panels/audio/Panel.qml

@@ -633,7 +633,7 @@ Panel {
     bar: root.bar
     text: root.outputIcon()
     onPressed: function(b) {
-      if (b === Qt.RightButton) root.toggleOutputMute()
+      if (b === Qt.RightButton) root.toggleAllMuted()
       else root.toggle()
     }