Remove browser tab mic indicator

by stopping micStream tracks

Author: microbit-grace

src/board/audio/index.ts

@@ -226,6 +226,7 @@ export class BoardAudio {
       recorder.disconnect();
       gain.disconnect();
       source.disconnect();
+      micStream.getTracks().forEach(track => track.stop())
       this.stopActiveRecording = undefined;
     };
   }