Shorten English title for 2FA to avoid line-break (#6001)

config/locales/en.yml

@@ -588,7 +588,7 @@ en:
     notifications: Notifications
     preferences: Preferences
     settings: Settings
-    two_factor_authentication: Two-factor Authentication
+    two_factor_authentication: Two-factor Auth
     your_apps: Your applications
   statuses:
     open_in_web: Open in web