Bug 1659847 - Explicitly set the showBookmarksToolbarAfterMigration pref so tests will continue to run after the feature is disabled. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D87980

browser/components/migration/tests/unit/xpcshell.ini

@@ -2,6 +2,8 @@
 head = head_migration.js
 firefox-appdir = browser
 skip-if = toolkit == 'android'
+prefs =
+  browser.migrate.showBookmarksToolbarAfterMigration=true
 support-files =
   Library/**
   AppData/**