Remove v-html from MR widget links component

Resolves #241863 (closed)

What does this MR do and why?

It replaces v-html with a safer alternative v-safe-html from app/assets/javascripts/vue_merge_request_widget/components/mr_widget_related_links.vue.

Note: There's one more v-html left in the aforementioned component. This will be refactored in a follow-up, see related discussion - !74696 (comment 744817680).

Screenshots or screen recordings

A quick test to confirm that the spec failure is valid and unrelated to this change

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.