**Issue:**
When a user posts a credit note with a currency exchange difference relative to the reversed move,
the resulting exchange move lines lack the mandatory analytic distribution.
This triggers a validation error, preventing the credit note from being posted.

**Steps to reproduce:**
- Set "mandatory" applicability on any analytic plan.
- Set two different currency rates on two different dates for any foreign currency.
- Create and post an invoice on the first date (ensure the mandatory analytic distribution is set).
- Create a credit note from that invoice using the second date.
- Click on the post button on the credit note.

Result: A validation error occurs even though the credit note itself has the mandatory analytic plan set,
because the auto-generated exchange move does not.

**Fix:**
Since the context key validate_analytic is set to True by the post button action,
it must be manually set to False during the automatic creation of exchange difference moves to bypass the mandatory plan check.

OPW-6081632

Forward-Port-Of: odoo/odoo#259624
Forward-Port-Of: odoo/odoo#259381