E2e new discussion not dropping MR from merge trains

What does this MR do?

New E2E test for feature #220916 (closed) , test case gitlab-org/quality/testcases#1010 (closed)

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content