Limits of the time machine feature (Z#23212144) (#5952)

* Add note about limits of the time machine feature
* Always check voucher validity against real time, not time machine time

src/pretix/presale/templates/pretixpresale/event/timemachine.html

@@ -20,6 +20,7 @@
                 {% bootstrap_form_errors timemachine_form "all" %}
 
                 <p>{% trans "Test your shop as if it were a different date and time." %}</p>
+                <p>{% trans "Please note that the changed time is not taken into account for aspects of the shop that affect quotas, such as the validity period of carts and vouchers." %}</p>
 
                 <div class="row">
                     <div class="col-md-6">
@@ -44,4 +45,4 @@
             <div class="clear"></div>
         </div>
     </div>
-{% endblock %}
+{% endblock %}