Change default value retrieval to use ToString method

The change was made in the DefaultExpressionDescriptorProvider.cs under Elsa.Workflows.Management. Instead of relying on the GetString method, the updated code now uses the ToString method for default value retrieval. This change improves how we process and retrieve default values in unspecified cases.

src/modules/Elsa.Workflows.Management/Providers/DefaultExpressionDescriptorProvider.cs

@@ -39,7 +39,7 @@ private ExpressionDescriptor CreateLiteralDescriptor()
  JsonValueKind.Number => elementValue.GetDecimal(),
  JsonValueKind.True => true,
  JsonValueKind.False => false,
- _ => v.GetString()
+ _ => v.ToString()
  });
 
  return new Expression("Literal", value);