Replace generic checkbox with GitLab UI styled checkbox in app/views/admin/application_settings/_repository_check.html.haml

What does this MR do and why?

The MR updates generic checkbox element to GitLab UI styled checkbox on the Admin -> Settings -> Repository page, Repository maintenance section.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Visit Admin -> Settings -> Repository page.
2. Select Repository maintenance section.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Review progress:

• UX review
• backend developer review
• backend maintainer review
• frontend developer review
• frontend maintainer review

Related to #358306 (closed)