Bug 1575185 - Skip test_permissions.html on fission; r=mccr8

Avoid high frequency intermittent failure on fission.

Differential Revision: https://phabricator.services.mozilla.com/D47693

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

dom/push/test/mochitest.ini

@@ -11,6 +11,7 @@ support-files =
 
 [test_has_permissions.html]
 [test_permissions.html]
+skip-if = fission # bug 1575185
 [test_register.html]
 skip-if = os == "win" # Bug 1373346
 [test_register_key.html]