Retry until 'The changes were merged' appears

What does this MR do?

Fixes qa/specs/features/ee/browser_ui/6_release/pipelines_for_merged_results_and_merge_trains_spec.rb:50 by retrying until 'The changes were merged' appears

Closes #33404 (closed)

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