[FIX] account: narration css overlap

Steps to reproduce:

- Open an invoice
- Enter a long link without spaces in the terms and conditions field
- Save

Issue:
The word doesn't break and spans outside its bounding box, possibly
overlapping with the subtotal footer on the right.

Solution:
Add class `text-break` to the narration field.

opw-3050054

closes odoo/odoo#106359

Signed-off-by: Grazioso Andrea (agr) <agr@odoo.com>