In `rollback_set_fcv.js`, we see there should be 3 topology version changes without FCV change when we transition to kSyncSourceOpsDuringRollback and kSteadyStateOps, including reconnect node, transition from primary to rollback and transition from rollback to secondary. When rolling back from upgrading to downgrading, FCV change should not increment topology version, but when rollback from downgrading to upgrading, there should be one increment. We should add a comment to the test explaining why there should be one more topologyVersion change in this case.