Use gl-button's outline variant in Dependency List alert

The Dependency List design uses the outline-danger button style for a button in one of its alerts.

The correct way to apply that would be to do something like:

<gl-button variant="outline-danger">

But that appears not to work currently, perhaps due to gitlab-org/gitlab-ce#49380.

This issue tracks the work to replace the workaround for the styling of the button in !13671 (merged), with the correct and documented markup above.