fix: correct SevenIO notification receiver field name (#6424)

Co-authored-by: Frank Elsinga <frank@elsinga.de>

server/notification-providers/sevenio.js

@@ -12,7 +12,7 @@ class SevenIO extends NotificationProvider {
         const okMsg = "Sent Successfully.";
 
         const data = {
-            to: notification.sevenioTo,
+            to: notification.sevenioReceiver,
             from: notification.sevenioSender || "Uptime Kuma",
             text: msg,
         };