[FIX]account: process one record to set debit/credit

Before this commit, There would be Expected singleton error
on changing Credit/Debit for multile account in single call.

Now, We are proocess one record to set `_set_opening_debit_credit`

closes odoo/odoo#69474

X-original-commit: 8fe9f552ed4591795b449f4d1e32e1563ce43ca2
Signed-off-by: William André (wan) <wan@odoo.com>

addons/account/models/account_account.py

@@ -284,10 +284,12 @@ class AccountAccount(models.Model):
             account.is_off_balance = account.internal_group == "off_balance"
 
     def _set_opening_debit(self):
-        self._set_opening_debit_credit(self.opening_debit, 'debit')
+        for record in self:
+            record._set_opening_debit_credit(record.opening_debit, 'debit')
 
     def _set_opening_credit(self):
-        self._set_opening_debit_credit(self.opening_credit, 'credit')
+        for record in self:
+            record._set_opening_debit_credit(record.opening_credit, 'credit')
 
     def _set_opening_debit_credit(self, amount, field):
         """ Generic function called by both opening_debit and opening_credit's