[FIX] account, account_sequence: psycopg2 errors class missing

Traceback when starting odoo server
ImportError: cannot import name 'errors' from 'psycopg2'

Exception management update in commit
4b430f8e
would require psycopg2 version 2.8 minimum but version in
requirements is 2.7.7

closes odoo/odoo#106345

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