Update Username input radius _border-radius.scss

Created by: SylvainBTL

Hello 👋, i noticed somes username input don't have same border radius :

• id="validationCustomUsername"
• id="validationServerUsername"
• id="validationTooltipUsername"

->https://getbootstrap.com/docs/4.4/components/forms/

I'm UX/UI designer so .. if you have better fix let me know ;)

Thanks, Sylvain