The TenantMigrationAccessBlocker can enter the committed or aborted states (kReject and kAborted, respectively) through a write unit of work onCommit handler or the op observer onMajorityCommitPointUpdate() listener. If these are interleaved, the access blocker may try to enter the same state twice, which triggers an invariant. Instead the methods for entering either state should early return if that state has already been entered.