Bug 23382: Use floating time zone to prevent tests to fail because of DST

Bug 23382: Use floating time zone to prevent tests to fail because of DST

Today Friday Oct 25th, DST next Sunday => Date math are wrong, 96 hours
diff becomes 95.
To avoid that we use the floating timezone

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit d4af82d411613f4d12d5e3e31de399aa43355cb4)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>