Bug 28509: Prevent Koha/Acquisition/Orders.t to fail randomly

Bug 28509: Prevent Koha/Acquisition/Orders.t to fail randomly

The random errors were:
03:25:39 koha_1       |     #     Structures begin differing at:
03:25:39 koha_1       |     #          $got->[0] = '10'
03:25:39 koha_1       |     #     $expected->[0] = '9'

and

16:36:15 koha_1       |     #     Structures begin differing at:
16:36:15 koha_1       |     #          $got->[0] = '100'
16:36:15 koha_1       |     #     $expected->[0] = '99'

You see it coming?

We sorted the ordernumbers alphabetically.

Test plan:
0. Don't apply this patch
1. % git checkout v21.05.01 # The error is not appearing in master right now
2. Add 2 warn statements before the 'The 2 orders are returned' tests to
display $order_1->ordernumber and $order_2->ordernumber
3. MariaDB CLI > ALTER TABLE aqorders AUTO_INCREMENT=3;
4. prove t/db_dependent/Koha/Acquisition/Orders.t
=> Fail with
    #     Structures begin differing at:
    #          $got->[0] = '10'
    #     $expected->[0] = '9'
5. Apply this patch, repeat 3. and 4.
=> The test passes now.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>