Bug 1591924 - Fix test_notifications_permission.html on beta r=tnguyen

Differential Revision: https://phabricator.services.mozilla.com/D50835

--HG--
extra : moz-landing-system : lando

dom/notification/test/mochitest/test_notification_permissions.html

@@ -22,6 +22,8 @@ add_task(async function test_notifications_permission() {
     set: [
       // Set pref to exercise relevant code path for regression test.
       ["permissions.delegation.enable", true],
+      // Automatically dismiss the permission request when it appears.
+      ["dom.webnotifications.requireuserinteraction", true],
     ],
   });