Fix HAML in shared/_label_row_epics_link.html.haml

What does this MR do?

Fixs HAML in ee/app/views/shared/_label_row_epics_link.html.haml simply to comply Layout/SpaceAfterColon in HAML-Lint.

Part of #326884 (closed)

Screenshots (strongly suggested)

n/a

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have not included a changelog entry because it is ~"technical debt" .
• Code review guidelines
• Style guides
• Separation of EE specific content