fix(RTC) Update sourceType on desktop track for web.

Fixes https://github.com/jitsi/jitsi-meet/issues/12319.

modules/RTC/JitsiLocalTrack.js

@@ -98,7 +98,7 @@ export default class JitsiLocalTrack extends JitsiTrack {
          */
         this.rtcId = rtcId;
         this.sourceId = sourceId;
-        this.sourceType = sourceType;
+        this.sourceType = sourceType ?? displaySurface;
 
         // Get the resolution from the track itself because it cannot be
         // certain which resolution webrtc has fallen back to using.