Bug 30007: (follow-up) Adapt tests

Bug 30007: (follow-up) Adapt tests

This patch adapts tests to acknowledge ->cancel and ->fill methods won't
yield 'undef' borrowernumber when anonymization takes place, and even
further, and exception will be thrown and cancellation/fulfillment will
be rejected.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Koha/Hold.t
=> SUCCESS: Tests pass!
3. Sign off :-D

Bonus: this problem was hidding bad tests caused by 29857, fixed on this
one as well.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>