[FIX] l10n_ch: write access to create invoices

- Having a user with access to create an invoice in Accounting, but
without the rights to create or modify Currency's objects;
- Install the Switzerland localization;
- Create an invoice with this user.

Before this commit, the user will have an access error. This issue arise
because when saving an invoice it will also try to save the name of the
currency. In the Switzerland localization a field(l10n_ch_currency_name)
is related to the currency's name of the invoice.

Now, this field is tagged as read-only, and when saving an invoice, it
won't try to save also the currency's name.

opw-2032756

closes odoo/odoo#34680

Signed-off-by: Nans Lefebvre (len) <len@odoo.com>

addons/l10n_ch/models/account_invoice.py

@@ -26,7 +26,7 @@ class AccountInvoice(models.Model):
     l10n_ch_isr_valid = fields.Boolean(compute='_compute_l10n_ch_isr_valid', help='Boolean value. True iff all the data required to generate the ISR are present')
 
     l10n_ch_isr_sent = fields.Boolean(defaut=False, help="Boolean value telling whether or not the ISR corresponding to this invoice has already been printed or sent by mail.")
-    l10n_ch_currency_name = fields.Char(related='currency_id.name', readonly=False, string="Currency Name", help="The name of this invoice's currency") #This field is used in the "invisible" condition field of the 'Print ISR' button.
+    l10n_ch_currency_name = fields.Char(related='currency_id.name', readonly=True, string="Currency Name", help="The name of this invoice's currency") #This field is used in the "invisible" condition field of the 'Print ISR' button.
 
     @api.depends('partner_bank_id.bank_id.l10n_ch_postal_eur', 'partner_bank_id.bank_id.l10n_ch_postal_chf')
     def _compute_l10n_ch_isr_postal(self):