Bug 1665713 - pt3 - fix js lint issues resulting from moving mochitest directory. r=ng

This was originally excepted under dom/media/tests/** here:
https://searchfox.org/mozilla-central/rev/89d33e1c3b0a57a9377b4815c2f4b58d933b7c32/.eslintrc.js#235

I'm adding the exception for dom/media/webrtc/tests/** for the moved files.

Differential Revision: https://phabricator.services.mozilla.com/D91344

.eslintrc.js

@@ -234,6 +234,7 @@ module.exports = {
         "dom/jsurl/**",
         "dom/media/tests/**",
         "dom/media/webaudio/**",
+        "dom/media/webrtc/tests/**",
         "dom/media/webspeech/**",
         "dom/messagechannel/**",
         "dom/midi/**",