[FIX] base: serialization bug when acquiring cron

Start Odoo with multiple cron threads (e.g. --max-cron-threads=4),
trigger many crons at once, there is a chance one of the cron thread
fails due to a serialization error.

Inside of the `_acquire_one_job` function, the query evaluates many rows
to find one that fit multiple requirements. Two of those requirements
are (1) that the `nextcall` of the row is in the past or (2) that it
exists a cron trigger for that cron with a `call_at` in the past.

In case the `nextcall` of one of those rows is modified or the cron
triggers are removed by another transaction then there can be a
serialisation failure in the current transaction. This serialisation
error is important, it prevents the current cron worker from acquiring a
cron job that has been processed in another cron worker.

The problem is that that postgres doesn't tell which row was modified by
the other transaction (=processed by another worker cron) so it is not
possible to just skip that cron and continue with the others.

Our solution is to limit the WHERE clause of the `_acquire_one_job`
function to a single row. In case there is a serialization failure we
know the cron was processed in another job and we can skip it.

Closes #96584

closes odoo/odoo#92387

Signed-off-by: Julien Castiaux <juc@odoo.com>
Co-authored-by: Julien Castiaux <juc@odoo.com>