[FIX] mass_mailing: Proper translation string

Computed expressions cannot happen inside a translation string.

closes odoo/odoo#34643

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

addons/mass_mailing/i18n/mass_mailing.pot

@@ -2285,9 +2285,9 @@ msgstr ""
 
 #. module: mass_mailing
 #. openerp-web
-#: code:addons/mass_mailing/static/src/js/unsubscribe.js:49
+#: code:addons/mass_mailing/static/src/js/unsubscribe.js:50
 #, python-format
-msgid "You have been <strong>successfully unsubscribed from </strong>."
+msgid "You have been <strong>successfully unsubscribed from %s</strong>."
 msgstr ""
 
 #. module: mass_mailing

addons/mass_mailing/static/src/js/unsubscribe.js

@@ -46,7 +46,10 @@ odoo.define('mass_mailing.unsubscribe', function (require) {
 
     var unsubscribed_list = $("input[name='unsubscribed_list']").val();
     if (unsubscribed_list){
-        $('#subscription_info').html(_t('You have been <strong>successfully unsubscribed from ' + unsubscribed_list + "</strong>."));
+        $('#subscription_info').html(_.str.sprintf(
+            _t("You have been <strong>successfully unsubscribed from %s</strong>."),
+            unsubscribed_list
+        ));
     }
     else{
         $('#subscription_info').html(_t('You have been <strong>successfully unsubscribed</strong>.'));