Bug 1915383 - Disable blocking third-party cookies for HeavyWeightFedCM tests. r=bvandersloot

Differential Revision: https://phabricator.services.mozilla.com/D220660

dom/credentialmanagement/identity/tests/mochitest/mochitest.toml

@@ -5,6 +5,7 @@ prefs = [
   "dom.security.credentialmanagement.identity.select_first_in_ui_lists=true",
   "dom.security.credentialmanagement.identity.reject_delay.enabled=false",
   "privacy.antitracking.enableWebcompat=false", # disables opener heuristic
+  "network.cookie.cookieBehavior.optInPartitioning=false", # disables blocking third-party cookies
 ]
 scheme = "https"
 skip-if = [