Quarantine two flaky specs

What does this MR do and why?

This MR quarantines two flaky specs reported in the below master-broken incidents:

• spec/lib/gitlab/seeders/ci/runner/runner_fleet_pipeline_seeder_spec.rb:31: gitlab-org/quality/engineering-productivity/master-broken-incidents#1055 (closed)
• ee/spec/features/epic_boards/new_epic_spec.rb:24: gitlab-org/quality/engineering-productivity/master-broken-incidents#1058 (closed)

Related to #394721 (closed) and #394693 (closed)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.