Update target frameworks
.NET Core 3.1, .NET 5.0 and .NET Framework 4.6.1 are all out of support now
Replace them with .NET 6 (LTS) which will be supported until November 12, 2024 and .NET Framework 4.6.2 which will be supported until Jan 12, 2027
Also drop .NET Standard 2.1 in favor of .NET 6.0 in the Ductus.FluentDocker project. The additional .NET Standard 2.1 target framework was not bringing anything substantial over .NET Standard 2.0. The .NET 6.0 at least will be beneficial for string interpolation. See also Are there benefits in producing a .NET 6.0 version of a .NET Standard 2.0 library? on Stack Overflow.
Thanks! :) - I'm merging when I get rid of gitversioning.tool and migrated from appveyor to GH workflows. I'll try to do it before end of October.
Cheers, Mario