"Index was outside the bounds of the array" OpenApiResponseWithBody List

Microsoft.Azure.Webjobs.Extensions.OpenApi 1.2.0
.NET Core 3.1

I tried
```c#
[OpenApiResponseWithBody(HttpStatusCode.BadRequest, MediaTypeNames.Application.Json, typeof(ValidationResponse))]
```
but got
```
Index was outside the bounds of the array.

at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Extensions.TypeExtensions.GetOpenApiSubTypeName(Type type, NamingStrategy namingStrategy)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Extensions.TypeExtensions.GetOpenApiDescription(Type type)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.Extensions.OpenApiResponseWithBodyAttributeExtensions.ToOpenApiResponse(OpenApiResponseWithBodyAttribute attribute, NamingStrategy namingStrategy, VisitorCollection collection, OpenApiVersionType version)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.DocumentHelper.<>c__DisplayClass7_0.b__1(OpenApiResponseWithBodyAttribute p)
at System.Linq.Enumerable.WhereSelectArrayIterator`2.MoveNext()
at System.Linq.Enumerable.ConcatIterator`1.MoveNext()
at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.Core.DocumentHelper.GetOpenApiResponses(MethodInfo element, NamingStrategy namingStrategy, VisitorCollection collection, OpenApiVersionType version)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.Document.Build(Assembly assembly, OpenApiVersionType version)
at Microsoft.Azure.WebJobs.Extensions.OpenApi.OpenApiTriggerFunctionProvider.RenderSwaggerDocument(HttpRequest req, String extension, ExecutionContext ctx, ILogger log)
```

The response type can be as easy as the following, as long as it is a collection.
```c#
public class ValidationResponse : List
{
}
```

When specifying directly it works, however I want to type it.

```c#
[OpenApiResponseWithBody(HttpStatusCode.BadRequest, MediaTypeNames.Application.Json, typeof(List))]
```

Start at TypeExtensions.GetOpenApiSubTypeName, using the stack trace from OpenApiResponseWithBodyAttributeExtensions.ToOpenApiResponse as the entry path. Reproduce the failure with a typed ValidationResponse collection and compare it with the working List case; done means the typed collection no longer throws while generating the OpenAPI response.

Written by the indexing model from the issue text.