[FIX] mass_mailing: deactivate snippet overlay on codeview

Before this commit, when toggling the codeview in mass_mailing (debug=1),
the overlay that highlights the selected snippet is not deactivated.
This results on the blue rectangle being seen on the codeview when the mouse
cursor is hovered over the corresponding position.

This commit deactivates the current snippet overlay when the codeview is
toggled.

closes odoo/odoo#115299

X-original-commit: ec8070adb38d092d743679c2dd30872424d46e9d
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>

addons/mass_mailing/static/src/js/mass_mailing_html_field.js

@@ -244,6 +244,7 @@ export class MassMailingHtmlField extends HtmlField {
             } else {
                 $codeview.val(this.wysiwyg.getValue());
             }
+            this.wysiwyg.snippetsMenu.activateSnippet(false);
             this.onIframeUpdated();
         });
         const $previewBtn = $snippetsSideBar.find('.o_mobile_preview_btn');