Bug 1397217 - Disable WebRTC ontonechange test for instability, a=testonly

MozReview-Commit-ID: 88EAMfYx6zd

testing/web-platform/meta/webrtc/RTCDTMFSender-ontonechange.html.ini

@@ -1,5 +1,6 @@
 [RTCDTMFSender-ontonechange.html]
   type: testharness
+  disabled: https://bugzilla.mozilla.org/show_bug.cgi?id=1397217
   [insertDTMF() with default duration and intertoneGap should fire tonechange events at the expected time]
     expected: FAIL