No headers on error response

[emckay]

When the server returns an error response, the response headers are added to the ClientError in rawRequest:

https://github.com/prisma-labs/graphql-request/blob/5b233c5658e65ed0d98cf8bff50beec413f399b9/src/index.ts#L71-L73

However, these headers are not added in request:

https://github.com/prisma-labs/graphql-request/blob/5b233c5658e65ed0d98cf8bff50beec413f399b9/src/index.ts#L104

In my application, I need to respond to errors differently based on the response headers, but I'd prefer not to use rawRequest.