Fix icon colors of related MRs widget

What does this MR do?

In CE related MRs widget, open and merged SVG icon colors were wrong. They were black.

This MR fixes the icon colors by making an EE-only code to both available in CE and EE.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry -Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content](https://docs.gitlab.com/ee/development/ee_features.html#separation-of-ee-code)

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/60249