[FIX] account: display amount due field in boxed layout

Versions:
---------
- 14.0+

Steps to reproduce:
-------------------
1. Settings -> Configure document layout
2. Select the Boxed layout
3. Go to Invoices -> create a new invoice and register payment
4. Click on Preview
5. The field “Amount due” is in the wrong color and barely visible

Issue:
------
The field “Amount due” is in the wrong color and barely visible in
invoice boxed layout

Cause:
------
The issue is happening because we have `<strong>`  before the text
”Amount due” and it changes the font color to gray because of the CSS definitions

Solution:
---------
We need to make the text bold in a different way, to do it we can use the bootstrap
class font-weight-bold, this way we keep it bold and do not break the colors

OPW-3374092

closes odoo/odoo#128451

Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>

addons/account/views/report_invoice.xml

@@ -174,8 +174,8 @@
                                                 </tr>
                                             </t>
                                             <t t-if="len(payments_vals) > 0">
-                                                <tr class="border-black">
-                                                    <td><strong>Amount Due</strong></td>
+                                                <tr class="border-black font-weight-bold">
+                                                    <td>Amount Due</td>
                                                     <td class="text-right">
                                                         <span t-field="o.amount_residual"/>
                                                     </td>