Update spinner in merge request status check to pajamas compliant

What does this MR do and why?

Updates the settings page merge request status check spinner to the pajamas compliant version. Addresses #353733 (closed).

Screenshots or screen recordings

New spinner	Old spinner

How to set up and validate locally

1. Either enable the external_status_checks feature or manually set this line to return true
2. Modify js-status-checks-settings to instead be js-status-checks-setting so that the Vue component it's tied to is unable to load
3. Navigate to http://localhost:3000/gitlab-org/gitlab-test/edit and expand the Merge Requests section
4. You should see Status checks available with a spinner
5. Change back to js-status-checks-settings and you should see the table load in normally.

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.