fix: keyerror due to my_tickets_url while rendering tickets template (#6858)

Used to send mails after tickets have been bought

Author: kushthedude

app/api/helpers/system_mails.py

@@ -190,7 +190,7 @@
             u"<br/>Your order has been processed successfully."
             + u"<br/> Your tickets & invoice have been enclosed."
             u"<br><br>You can also download your tickets in <b>My Tickets</b> section."
-            u"<br/>Login to manage the orders at <a href='{mytickets_url}' target='_blank'>{mytickets_url}</a> </em>"
+            u"<br/>Login to manage the orders at <a href='{my_tickets_url}' target='_blank'>{my_tickets_url}</a> </em>"
             u"<br><br><em>Looking forward to seeing you at the event."
         ),
     },