Update MR widget icon size

Problem

The level one status icon of the merge request widget is using s16 (16px) when it should be s12 (12px).

Solution

It's difficult to determine from the specs, but the design uses a 12px icon surrounded by a 2px border of the same color to total 16px. It's a bit more clear in Figma. This was done so that icon sizes could be consistent throughout the widget, but also so the dimensions of the level one align with the other levels. It's likely necessary to have a background behind the icon so that the knock-out portion remains visible.

Current	Specs