Describe the bug

When deserializing to a class with both nullable reference and value types members, YamlDotNet considers the nullabe value type to not accept null values.

I suspect it's coming from the reflection checks only checking if a member allows null using the presence of NullableAttribute, which fails if it's a TValueType? (this won't generate a NullableAttribute). But I've seen strange cases where the compiler doesn't even generate NullableAttribute on a reference type, so I won't be too sure about that.

To Reproduce
Using latest version: 16.2.1

Create a new console project with .net8
Program.cs

#nullable enable
using YamlDotNet.Serialization;

var deserializer = new DeserializerBuilder().WithEnforceNullability().Build();
var yaml = @"
TestString: null
TestBool: null
";
var test = deserializer.Deserialize<NonNullableClass>(yaml);

public class NonNullableClass
{
    public string? TestString { get; set; }
    public bool? TestBool { get; set; }
}

Result:

Unhandled exception. (Line: 2, Col: 1, Idx: 2) - (Line: 2, Col: 11, Idx: 12): Strict nullability enforcement error.