Upgrade gitlab-ui once source code is moved to src/ directory

What does this MR do?

This MR addresses the breaking changes that were introduced in gitlab-ui@7.0.0 where all source files were moved to a src/ directory (gitlab-ui!847 (merged)).

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