chore: apply new generated enumeration readonly modifier

to the template 'Configuration' enum in new GRUKE projects; also use target-typed new for it, as the default build project is .NET 10.

Author: GreemDev

source/Nuke.GlobalTool/templates/Configuration.cs

@@ -6,8 +6,8 @@
 [TypeConverter(typeof(TypeConverter<Configuration>))]
 public class Configuration : Enumeration
 {
-    public static Configuration Debug = new Configuration { Value = nameof(Debug) };
-    public static Configuration Release = new Configuration { Value = nameof(Release) };
+    public static readonly Configuration Debug = new() { Value = nameof(Debug) };
+    public static readonly Configuration Release = new() { Value = nameof(Release) };
 
     public static implicit operator string(Configuration configuration)
     {