Update dependencies

* Add support for C# 12
* Run all tests on all major .NET SDKs
* Only build on Ubuntu
* Do not build docs for pull requests
* Add Cédric Luthi, and Frank Ray to authors
* Drop netstandard2.0 for ImageSharp plugin

test/Spectre.Console.Cli.Tests/Data/Commands/TurtleCommand.cs

@@ -5,7 +5,6 @@ public class TurtleCommand : AnimalCommand<TurtleSettings>
 {
     public override int Execute(CommandContext context, TurtleSettings settings)
     {
-        DumpSettings(context, settings);
         return 0;
     }
 }