Remove several tests from quarantine at once, from the Mitigation page

The Mitigation page lists the tests currently in quarantine. Until now, removing several of them at once was only possible from Detection, the page that lists unhealthy tests — so cleaning out stale quarantines meant finding each test there first.

Mitigation now lets you tick several quarantined tests and remove them from quarantine in one action. The list and the quarantine figures update in place.

Pull request: https://github.com/Mergifyio/monorepo (MRGFY-9440, number set once opened)