Bug 19693: (QA follow-up) Replace changed tag test

Bug 19693: (QA follow-up) Replace changed tag test

The test
  $MARCfrom->field('1..', '2..'))[0]->tag ne ($MARCto->field('1..', '2..'))[0]->tag
is not completely consistent with following code in sub merge.
I decided to get the authtype code from the old record that comes
from Koha and should include the type.
Remaining changes refer to indentation/comments.

Test plan:
Run t/db_dependent/Authority/Merge.t
Note: The test actually could be extended a bit for mocking MARC
flavor, but needs some additional framework support to work.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>