Differentiate tests expanded MR widget

This is an actionable insight from the UX Department: MRs experience async critique research (insight).

In the merge request widget for code tests, there's no visual difference between the widget's header and its expanded content.

Visually differentiate the MR widget header from the expanded content.

Figma Design Note that these are the same designs uploaded to #293655 (closed)

Edited Feb 19, 2021 by Scott Hampton