Bug 17124: Fix tests in DecreaseLoanHighHolds.t

Bug 17124: Fix tests in DecreaseLoanHighHolds.t

One test of DecreaseLoanHighHolds.t does not pass,
A hashref representing a patron has a 'borrower' key defined, instead of
'borrowernumber'.

Test plan:
  prove t/db_dependent/DecreaseLoanHighHolds.t
must return green

Signed-off-by: Claire Gravely <claire_gravely@hotmail.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 1bc34e31e9c371d8f60a074f13e933d15a31e20e)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>