GitHub thread about the error - and long and winding discussion about the topic.

How to resolve build failing with .NET Core 3 and Microsoft.AspNetCore.Mvc.Versioning

Building a proof-of-concept on .NET Core 3.0 preview 7 I ran into issues when developing web APIs. This release is production-ready (according to Microsoft -see below), but every now and then you run into really unintuitive and sometimes surprising issues. Go LiveNET Core 3.0 Preview 7 is supported by Microsoft and can be used in production. We strongly recommend that you test your app running on Preview 7 before deploying…Continue reading How to resolve build failing with .NET Core 3 and Microsoft.AspNetCore.Mvc.Versioning