Bug 11439: (follow up) add missing rollback call

Bug 11439: (follow up) add missing rollback call

This UT got wrapped inside a transaction with autocommit=0 but
the rollback call was inadvertedly ommited. Adding it.

[RM note: an explicit rollback is not required, as the
 transaction will roll back automatically at the end of
 the DB session. Nonetheless, it hurts nothing to have
 it be explicit.]

Sponsored-by: Universidad Nacional de Cordoba
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>