Bug 17573: Remove itemtype-related warnings from DecreaseLoanHighHolds.t

Bug 17573: Remove itemtype-related warnings from DecreaseLoanHighHolds.t

To test:
- Run:
  $ prove t/db_dependent/DecreaseLoanHighHolds.t
=> FAIL: Lots of warnings
- Apply the patch
- Run:
  $ prove t/db_dependent/DecreaseLoanHighHolds.t
=> SUCCESS: All green and no warnings.
- Sign off :-D

Sponsored-by: ByWater Solutions
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Mason James <mtj@kohaaloha.com>