Stablize editing scope label spec - retry if dropdown is not visible

What does this MR do?

Stablize editing scope label spec - retry if dropdown is not visible

CE Port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/31145

Closes: https://gitlab.com/gitlab-org/quality/nightly/issues/117

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