Quarantine pull mirroring spec while we investigate the issue

What does this MR do?

Quarantine pull_mirroring_over_ssh_with_key_spec while the issue is investigated as the test is consistently failing on master, nightly and staging.

Related to #216297 (closed)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

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