Make it clearer what internal TimersDescriptionAttribute ctor is for (#51075)

src/libraries/System.ComponentModel.TypeConverter/src/System/Timers/TimersDescriptionAttribute.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.ComponentModel;
+using System.Diagnostics;
 
 namespace System.Timers
 {
@@ -23,7 +24,11 @@ public class TimersDescriptionAttribute : DescriptionAttribute
         /// <summary>
         /// Constructs a new localized sys description.
         /// </summary>
-        internal TimersDescriptionAttribute(string description, string defaultValue) : base(SR.GetResourceString(description, defaultValue)) { }
+        internal TimersDescriptionAttribute(string description, string unused) : base(SR.GetResourceString(description))
+        {
+            // Needed for overload resolution
+            Debug.Assert(unused == null);
+        }
 
         /// <summary>
         /// Retrieves the description text.