[FIX] account: automatic entry wizard: avoid clashes with lock dates

Currently, if you use the automatic entry wizard to change the period of
a journal item dated prior to the lock date, you'll just get blocked
with a UserError, with no workaround.

This commit changes the date of the adjustment entry to be the first end
of month after the lock date. As a result, the adjustment entry can be
created.

Based on PR #92439

closes odoo/odoo#121566

Taskid: 2823170
Signed-off-by: William André (wan) <wan@odoo.com>