Bug 16609: Catch warning from Koha::Hold in Hold.t

Bug 16609: Catch warning from Koha::Hold in Hold.t

Before this patch, the suspend step triggers a warn from Koha::Hold.
Now we catch it.

Test plan:
Run the test. Do not see the warning about unable to suspend.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
NOTE: Nice clean up!

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>