Add pretty tests for UnscopedRef members

UnscopedRef only appeared on a params parameter anywhere in the
suite; a ref-returning method and property on a ref struct pin the
attribute round-trip.

Assisted-by: Claude:claude-fable-5:Claude Code

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

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
@@ -84,4 +85,18 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			Field3 = ref v;
 		}
 	}
+
+	internal ref struct UnscopedRefStruct
+	{
+		private int val;
+
+		[UnscopedRef]
+		public ref int ByRefProperty => ref val;
+
+		[UnscopedRef]
+		public ref int ByRefAccess()
+		{
+			return ref val;
+		}
+	}
 }