At this moment all I can say is that the [sys].[ipv6_database_firewall_rules] view is not related to any current feature or setting in use by Azure SQL Azure. Maybe in the future it could be related to new Azure SQL database features. So the finding can be dismissed as Azure SQL database cannot listen on IPv6 at the moment.
You can also revoke any permissions granted to PUBLIC on that object to avoid this finding to appear on VA assessments.