[FIX] account_payment: fix payment modal issue

purpose of this commit is to show modal with proper height

before this commit:
currently,  the modal structure was not correct, so it is displaying
modal-content twice in the modal that's why it shows modal with full height.

after this commit:
correct modal structure to show it properly, so payment modal in the portal view
looks like as expected.

task-2025869
closes: https://github.com/odoo/odoo/pull/34334

closes odoo/odoo#34334

Signed-off-by: Damien Bouvy (dbo) <dbo@odoo.com>

addons/account_payment/views/account_portal_templates.xml

@@ -38,7 +38,7 @@
     <template id="portal_invoice_payment" name="Invoice Payment">
         <div class="row" t-if="not tx_ids and invoice.state == 'open' and invoice.amount_total" id="portal_pay">
             <div class="modal fade" id="pay_with" role="dialog">
-                <div class="modal-dialog modal-content">
+                <div class="modal-dialog">
                     <div class="modal-content">
                         <div class="modal-header">
                             <h3 class="modal-title">Pay with</h3>