De-quarantine e2e test for issue suggestions

What does this MR do?

De-quarantine issue_suggestions_spec.rb.

Closes gitlab-org/quality/staging#53 (closed).

Does this MR meet the acceptance criteria?

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