ignore transcriptions from previous turns of conversation (#734)

lib/tasks/gather.js

@@ -747,6 +747,7 @@ class TaskGather extends SttTask {
     const finished = fsEvent.getHeader('transcription-session-finished');
     this.logger.debug({evt, bugname, finished, vendor: this.vendor}, 'Gather:_onTranscription raw transcript');
     if (bugname && this.bugname !== bugname) return;
+    if (finished === 'true') return;
 
     if (this.vendor === 'ibm' && evt?.state === 'listening') return;
     if (this.vendor === 'deepgram' && evt.type === 'UtteranceEnd') {