[FIX] account: missing dependancy on constraint

It was possible to create inconstancies in accounting entries by forcing to sum apples and pears.

Steps to reproduce
1. create a journal entry using at least one account with a secondary currency set
2. balance and save that move
3. change the secondary currency on the line and force it to a different value than the one on the account
4. save. You'd expect an error pop up but the constraint doesn't trigger and you're allowed to save/post

opw-3340697

closes odoo/odoo#126231

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