A flaky test quarantine with a deadline attached

A group of tests excluded from the pipeline “temporarily”, four of them since 2021.

<groups>
  <exclude>
    <group>flaky</group>
  </exclude>
</groups>

<!-- and the rule that made it work: a quarantined test
     carries a ticket and a date in its attribute -->
#[Group('flaky')]
#[Ticket('ENG-412', until: '2023-03-01')]

A quarantine without an expiry is a delete with extra steps. Adding a date and a weekly job that fails the build when one passes turned a list of eleven into a list of two within a month — six were fixed, three were deleted because the behaviour they tested had been removed, and the two that remain are genuinely hard and have owners.