Bug 30536: Unit tests

Bug 30536: Unit tests

This patch adds tests to make sure there's no behavior change regarding
error conditions. When requests include wrong x-koha-embed values, a 400
error should be returned, both in our original implementation or relying
on the Mojolicious::Plugin::OpenAPI features.

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/query.t
=> SUCCESS: Tests pass
3. Apply the rest of the patches
4. Repeat 2
=> SUCCESS: Tests still pass
5. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>