Explicitly set contentType to avoid promotion to jsonp

Signed-off-by: DL6ER <dl6er@dl6er.de>

scripts/pi-hole/js/settings-system.js

@@ -298,6 +298,7 @@ $("#loggingButton").confirm({
       type: "PATCH",
       dataType: "json",
       processData: false,
+      contentType: "application/json; charset=utf-8",
       data: JSON.stringify(data),
     })
       .done(function (data) {