Issue #3615469: Move 'page' inside the user login link on the maintenance mode form

Moves the word "page" inside the user login link on the maintenance mode settings form so the link text is the complete phrase "user login page", fixing the WCAG 2.4.4 link-purpose weakness and the "user loginpage" run-together in the checkbox's accessible description. Updates the SiteMaintenanceTest link assertion to match. See https://www.drupal.org/project/drupal/issues/3615469