Fix Epics filter search bar dropdown alignment

What does this MR do?

Fixes filter dropdown alignment on Epics list page

Screenshots

Before	After

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://gitlab.com/gitlab-org/gitlab-ce/issues/45864

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/30120