[FIX] account: change journal on journal entry

With this commit, we make sure that the name
of an entry is well computed when changing
the journal in the form view.

Steps:

- With fresh db
- Open a new journal entry form
- Change the journal
-> The name doesn't change, it should change
   regarding the code of the journal

Also add a test for the fix which introduced
the issue 46e6ae29.

opw-3332590

closes odoo/odoo#122505

Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>