Add net6.0-windows for supported TargetFrameworks

[i2van]

Please add net6.0-windows for supported TargetFrameworks, i.e.

<TargetFrameworks>net452;net462;net472;net48;netcoreapp3.1;net5.0-windows;net6.0-windows</TargetFrameworks>

[johnthagen]

This has been fixed in the new active fork:

• Microsoft-WindowsAPICodePack 6.0