Add missing classes to omniauth remember-me checkbox and add correct font-size

What does this MR do?

This is a fix for the issue reported at

Are there points in the code the reviewer needs to double check?

I made the markup consistent with the top remember me checkbox as they looked like generic classes in form.scss Can add them as distinct classes if that isn't the case.

Screenshots (if relevant)

Before: before

After: gitlab-ui-polish-remember-me

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Edited by username-removed-507451

Merge request reports