Bug 20287: Use more simple object for Object.t

Bug 20287: Use more simple object for Object.t

We initially use Koha::Patron to test Object.t, but now it overwrites
->store and so it is better to use a more simple object.
ApiKey has foreign keys and unique key.
We lost one test: there is only one unique key whereas we had 2 on
borrowers (I did not find a better option)

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>