Nuget update to flag Dotnet6 support

[Paul Sweeney]

As per title, can the nuget package be updated (or a new submission made if updating that one is not possible) to include the fact that Dotnet6 is supported?

The current nuget version actually seems to work ok, but I'm getting warnings in vscode because it doesn't declare that it supports dotnet6, e.g. the microsoft C# plugin reports errors on load and outputs:

Error: Package 'NativeMessaging 2.0.0' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,Version=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8, .NETFramework,Version=v4.8.1' instead of the project target framework 'net6.0-windows7.0'. This package may not be fully compatible with your project.

and dotnet build gives:

warning NU1701: Package 'NativeMessaging 2.0.0' was restored using '.NETFramework,Version=v4.6.1, .NETFramework,V
ersion=v4.6.2, .NETFramework,Version=v4.7, .NETFramework,Version=v4.7.1, .NETFramework,Version=v4.7.2, .NETFramework,Version=v4.8, .NETFramework,Version=v4.8.1' instead of the  
project target framework 'net6.0-windows7.0'. This package may not be fully compatible with your project.

Thanks!