The "Log in" and "Register" actions were being displayed as default list items in the mobile menu.
This adds the rb-c-page-sidebar__mobile-user-actions class to the unordered list for users that are not authenticated so the actions will be displayed with the proper styling.

Ran with ./contrib/internal/devserver.py.
Verified in mobile-view in Chrome that the actions are shown as commands along the top instead of default list styling as before.