Bug 23234: Mock DateTime->now using the time zone

Bug 23234: Mock DateTime->now using the time zone

The timezone of the two dt was different, one was UTC, the other one was
my local one.
When we mocked DateTime->now we did not use the time zone, we must use
dt_from_string instead

Test plan:
Make sure your environment has a different time zone than UTC
`prove t/db_dependent/Circulation.t` should fail without this patch

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit 549a09c52178937af28cc11c5bfa7f00cbced1b5)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>