Bug 18697: Adjusting unit tests for dayly serial frequencies

Bug 18697: Adjusting unit tests for dayly serial frequencies

No changes were needed for GetNextDate.t.
In GetFictiveIssueNumber.t we add a subtest for daily frequencies.

Test plan:
[1] Run t/db_dependent/Serials/GetFictiveIssueNumber.t

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>