Bug 16010: follow-up of 15381 - FIX merge_authorities migration script

Bug 16010: follow-up of 15381 - FIX merge_authorities migration script

Caused by commit 7e70202d34d75f988fbaea9b911347417c203aac
    Bug 15381: Remove GetAuthType and GetAuthTypeCode

If you execute perl misc/migration_tools/merge_authority.pl -f 1 -t 2
you will get:
Can't locate object method "authtypecode" via package "1" (perhaps you forgot to load "1"?)
 at misc/migration_tools/merge_authority.pl line 58.

GetAuthority does not return a Koha::Authority but a MARC::Record:
there is no authtype code method!

Test plan:
perl misc/migration_tools/merge_authority.pl -f X -t Y
Should not return any error.
Note that if the authid X or Y does not exist, the script will die.

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com