Change variant to confirm for approve button

What does this MR do and why?

Updates the variant to confirm to match Pajamas guidelines

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to /admin/users and choose a user
2. Click the "Impersonate" button in the upper right corner
3. Navigate to the newly created group "Overview" page and click the "Request access" link next to the group name
4. Stop impersonation in the upper right corner
5. Navigate to "Group" -> "Members" and click the "Access requests" tab

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.