GraphQL.Convention.Optional<T> invalid name for T : Array

## Description

Schema generated error for Optional where T is an array.

### Steps to reproduce

Declare input with property Optional MyProp {get;set;}

public record MyInput
{
public Optional Items { get; set; }
}

### Expected result

Correctly generated schema.

### Actual result

Exception:
A type name must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but 'MyClass[]Optional' does not. (Parameter 'name')