Add test case for C# 12 optional parameters in lambdas.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/OptionalArguments.cs

@@ -24,6 +24,8 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
 	internal class OptionalArguments : List<int>
 	{
+		public delegate int D(int p = 10);
+
 		public enum MyEnum
 		{
 			A,
@@ -283,5 +285,18 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 		}
 #endif
+
+#if CS120
+		public static D LambdaWithOptionalParameter()
+		{
+			return (int x = 10) => x;
+		}
+
+		public static void Use(D d)
+		{
+			d();
+			d(42);
+		}
+#endif
 	}
 }