Fix the build for VS2022 by altering the arguments to ArgumentException

Why: Currently this project does not build for users of VS2022 because of CA2208.

Author: pauldendulk

samples/snippets/core/testing/unit-testing-best-practices/csharp/unit-testing-best-practices/StringCalculator.cs

@@ -10,7 +10,7 @@ public int Add(string numbers)
         {
             if (numbers == null)
             {
-                throw new ArgumentException(nameof(numbers));
+                throw new ArgumentNullException(nameof(numbers));
             }
 
             int result;
@@ -49,7 +49,8 @@ private static int HandleSingleNumber(string number)
             var result = int.TryParse(number, out var parsedNumber);
             if (result == false)
             {
-                 throw new ArgumentException(nameof(number));
+                throw new ArgumentException(
+                    $"Unable to parse {nameof(number)} as an Int32.", nameof(number));
             }
 
             return parsedNumber;