Fix layout for a banner on personal page project creation

What does this MR do and why?

Stuff that should Just Work — fixes layout and margin for a banner when creating a README project for the GitLab profile page.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

• Go to project creation page (http://localhost:3000/projects/new#blank_project)
• in "Project slug" type in your profile name (root for admins)
• see the banner appear below the field