Bug 36100: Update unit tests for add

Bug 36100: Update unit tests for add

This patch updates the unit tests for booking add to confirm that
without readOnly we still return an error should a user attempt to
submit a booking with a booking_id that would clash.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit d810b3663bf855101d75673abc77d05bf65596dd)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>