Bug 28445: Add diag for failing test

Bug 28445: Add diag for failing test

Temporary patch to help trying to fix the following random error:
     #   Failed test 'Item types should be sorted by description and an empty entries should be shown'
     #   at t/db_dependent/Koha/UI/Form/Builder/Item.t line 121.
     #     Structures begin differing at:
     #          $got->[12] = 'Be9T9FH5aO'
     #     $expected->[12] = 'REF'
     # Looks like you failed 1 test of 2.

 #   Failed test 'itemtypes'
 #   at t/db_dependent/Koha/UI/Form/Builder/Item.t line 130.

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