Attach ticekts to "order approved" email if possible

src/pretix/base/services/orders.py

@@ -315,6 +315,7 @@ def approve_order(order, user=None, send_mail: bool=True, auth=None, force=False
                 order.send_mail(
                     email_subject, email_template, email_context,
                     'pretix.event.order.email.order_approved', user,
+                    attach_tickets=True,
                     invoices=[invoice] if invoice and order.event.settings.invoice_email_attachment else []
                 )
             except SendMailException: