Update variant expected-result file.
This should have been updated in
d2d8a229b, but it was overlooked.
According to
31a877f18 which added it, this file is meant to show the
results you get under default_transaction_isolation = serializable.
We've largely lost track of that goal in other isolation tests, but
as long as we've got this one, it should be right.
Noted while fooling about with the isolationtester.