I upgraded to Skype 8.11 from 7.x and found that I am now getting audio notifications when I receive a chat message. In the previous version of Skype you had fine-grained control over the notification sounds and I had almost all of them disabled. In this version of Skype that option appears to have been removed.
In my application settings I only have 'Chat notifications' enabled; 'In-app notifications', and 'In-app sounds' and turned off.
I have also turned off 'Play sounds for notifications' in Mac Notification settings:
I am running macOS High Sierra (10.13.1).
How can I disable these sounds?