[FIX] account: clearer bank account holder validation message

Steps:
- Go to Accounting > Configuration > Accounting > Bank Accounts
- Create a new Bank Account
  - "Bank Account" field: create and edit a new one
    - Account Holder: Anyone but your company
- Save

Bug:
Validation Error: The holder of a journal's bank account must be the
company (YourCompany).

Explanation:
The error is not clear enough. Users may be confused because this
validation error appears upon saving a "Bank Account Journal"
(`account.journal`) but is talking about "Partner Bank Account"
(`res.partner.bank`) which is a field of the "Bank Account Journal".

opw:2448183

closes odoo/odoo#65281

Signed-off-by: backspac <backspac@users.noreply.github.com>