[FIX] sale_coupon: remove em tag from report

In master, em tag are not displayed in PDF report.
Strangly, the space to display the element is taken but the element content is
invisible.
If the action report is change from PDF to HTML, the element is displayed as it
should, in italic.

As having `Code:` in italic is not that mandatory, this commit removes the em
tag to display `Code:` again.

closes odoo/odoo#35685

Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>

addons/sale_coupon/report/sale_coupon_report_templates.xml

@@ -44,7 +44,7 @@
                                     <strong t-field="o.expiration_date" t-options='{"format": "d MMMM y"}'/>
                                 </h3>
                                 <h3>
-                                    <em>CODE :</em>
+                                    CODE:
                                     <strong class="bg-success" t-esc="o.code"></strong>
                                 </h3>
                                 <h4 t-if="o.program_id.rule_min_quantity > 1">