fixes https://linear.app/tryghost/issue/SLO-121 fixes https://linear.app/tryghost/issue/SLO-138 fixes https://linear.app/tryghost/issue/SLO-139 fixes https://linear.app/tryghost/issue/SLO-140 fixes https://linear.app/tryghost/issue/SLO-141 fixes https://linear.app/tryghost/issue/SLO-142 - ember-concurrency prevents two executions of the same task from running at the same time - when a task is cancelled, the library raises an error by default - however, we don't need to surface that error as the cancellation of the second execution is intentional