[FIX] account: update currency rate when duplicating move

Setup multicurrency, with:
* rateA for dateA
* rateB for dateB (dateB > dateA)

Have an invoice in dateA with foreign currency and duplicate it.
Checking the journal entries, you should see that Debit/Credit is the
same as the source invoice. Posting the invoice would assign today date,
keeping the wrong rate.

opw-3007740

Backport of 0ac6bb4662b537ed10eaab89a6484476c421342f

closes odoo/odoo#106146

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