Asp.Net Core attribute validation does not work on polymorphic properties

### Description

If the property of the validated request is polymorphic, the validation would not work.

### Reproduction Steps

```csharp
using System.ComponentModel.DataAnnotations;
using System.Text.Json.Serialization;
using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
var app = builder.Build();

app.MapControllers();

app.Run();

[ApiController]
public class TestController : ControllerBase
{
[HttpPost("test-property")]
public void Test(Request request) { }

[HttpPost("test-request")]
public void Test(Base request){ }
}

public record Request
{
public required Base Prop { get; init; }
}

[JsonPolymorphic(TypeDiscriminatorPropertyName = "type")]
[JsonDerivedType(typeof(Derived), "derived")]
public abstract record Base { }

public record Derived : Base
{

[Required, StringLength(1)]
public string? Field { get; init; }
}
```

One can use this code with these two payloads:

This request to "test-property" results in 200 (which is incorrect since the field "field" is not specified):
```json
{
"prop": {
"type": "derived"
}
}
```

while a request to "test-request" results in 400 ("The Field field is required." which is correct):
```json
{
"type": "derived"
}
```

### Expected behavior

400 error and Validation of the Derived class properties even if it is a property of the original model.

Please note that without polymorphism (i.e. using Derived class directly instead of Base for Prop the validation works as expected.

### Actual behavior

The Prop is not validated and 200 is returned

### Regression?

_No response_

### Known Workarounds

_No response_

### Configuration

.Net 8

### Other information

This issue came out of issue dotnet/runtime#98430 where another bug was identified for the `Validator` class (which does not go into properties at all). It was a suggestion by @eiriktsarpalis to split this bug into a separate one.

And just to avoid confusion: this is not a problem with System.Text.Json but with the ASP.Net Core validation of models and how they traverse the object being validated.