Bug 11912: (follow-up) Use the common way to mock syspref

Bug 11912: (follow-up) Use the common way to mock syspref

t::lib::Mocks::mock_preference provides a simple way to mock syspref.

Test plan:
Verify that t/db_dependent/Biblio.t returns green.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit c5f8bf244b9db2e3279774435ae75f7c4b4ab68a)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 11a890df5ab01c504d799d813f70cd6c841379b3)