Adjust size and align MR-widget loading icon

What does this MR do?

A recent change within gitlab-ui introduced a new size (24x24) to the loading-icon component.

This MR changes the the loading-icon's new size (24x24) to bring it to the same dimensions as the status-icon and applies some styling to vertically align them.

Before

After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.

Performance and testing

• Tested in all supported browsers

Closes #62609 (closed)