Adding CC and BCC in the notification either from the event parameter or by explicitly mentioned in the script is not working.
This issue is because of the fact that the property "glide.email.test.user" has the value with an email address.
If "glide.email.test.user" property is set then ServiceNow only set the "To" Recipient in the Email Headers even if the configurations are for CC and BCC field over the script it will be disregarded.
If this property is set to empty value then we set To / CC / BCC as well. Please empty this property to achieve populating CC and BCC.