Audit usage of link variant in ee/app/assets/javascripts/roadmap/components/milestones_list_section.vue

We updated our styling of the link variant button to represent a link (blue text). With this change, we also introduced a new button category (tertiary), which are styled as secondary buttons without a background or border. Prior to this change, the link variant was often used in cases where a button was needed without a border. We now need to audit the use of the link variant throughout the app and determine whether the button should continue using the link styling or be migrated to a tertiary button.

Review the following file in the title and determine whether the button(s) in this file that are using a link variant should continue using a link or be migrated to a tertiary button.