Resolve "Arrow for linked pipeline has the wrong color"

What does this MR do?

Fixes arrow-icon color and alignment in linked pipeline in merge request widget

Screenshots

before	after

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary

• Conform by the code review guidelines

  • Has been reviewed by a Frontend maintainer

• Conform by the merge request performance guides

• Conform by the style guides

What are the relevant issue numbers?

Closes #6807 (closed)