Bug 28585: (QA follow-up) Fix object.t

Bug 28585: (QA follow-up) Fix object.t

Object.t was still testing for the return of DateTime objects from
attributes_from_api. I checked all calls to attrbutes_from_api for
reliance of DateTime objects and confirmed they all get passed into
search calls and thus are better served as SQL formatted strings.

I then converted the test to check that the rfc3339 formatted dates
passed in were converted to strings appropriate for feeding into SQL
where statements instead.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
JD amended patch:
  FAIL   spelling
    formated ==> formatted

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>