var validator = _serviceCollection.BuildServiceProvider()
     .GetService(validatorType);

namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
public class ModelValidatorProviderContext
{
    public ModelValidatorProviderContext(ModelMetadata modelMetadata, IList<ValidatorItem> items)
    {
        ModelMetadata = modelMetadata;
        Results = items;
    }
    public ModelMetadata ModelMetadata { get; set; }
    public IReadOnlyList<object> ValidatorMetadata => ModelMetadata.ValidatorMetadata;
    public IList<ValidatorItem> Results { get; }

    // this is the new method
    object? IServiceProvider GetService(type type);
}

 object? IServiceProvider GetService(type type);

 var validatorType = typeof(IValidator<>).MakeGenericType(
     context.ModelMetadata.ModelType);
var object = context.GetService(validatorType)

public class ModelValidatorProvider : IModelValidatorProvider
{
  // now no need for constructor at al here

    public void CreateValidators(ModelValidatorProviderContext context)
    {
        var validatorType = typeof(IValidator<>).MakeGenericType(
            context.ModelMetadata.ModelType);

  // here is the usage of the new method
        var validator = context.GetService(validatorType)

        if (validator != null)
        {
            var simpleValidatorType = typeof(ModelValidator<>).MakeGenericType(context.ModelMetadata.ModelType);

            var simpleValidator = (IModelValidator?)Activator.CreateInstance(simpleValidatorType, validator);

            context.Results.Add(new ValidatorItem
            {
                IsReusable = true,
                Validator = simpleValidator
            });
        }
    }