fix: use TTS_FAILURE alert type for synthAudio

lib/tasks/say.js

@@ -143,7 +143,7 @@ class TaskSay extends Task {
           span.end();
           writeAlerts({
             account_sid: cs.accountSid,
-            alert_type: AlertType.TTS_NOT_PROVISIONED,
+            alert_type: AlertType.TTS_FAILURE,
             vendor,
             detail: err.message
           }).catch((err) => this.logger.info({err}, 'Error generating alert for tts failure'));