Bug 1737670 - Part 4: Skip xorigin test for dFPI in serviceworkers. r=asuth

Currently, the third-party service worker is disabled in dFPI. So, it
makes no sense to run xorigin tests for dFPI.

Differential Revision: https://phabricator.services.mozilla.com/D130891

dom/serviceworkers/test/mochitest-dFPI.ini

@@ -3,6 +3,9 @@
 prefs =
   network.cookie.cookieBehavior=5
 tags = serviceworker-dfpi
+# We disable service workers for third-party contexts when dFPI is enabled. So,
+# we disable xorigin tests for dFPI.
+skip-if = xorigin
 dupe-manifest = true
 
 [include:mochitest-common.ini]