Test case 6.4 must allow response

[ThetaSinner]

Test case 6.4 sends a headers frame with end_headers and end_stream set. That means the server is allowed to produce and response and queue the response for sending. The server is not obliged to check for a reset stream arriving before queuing the response for sending. The test should either:

• Not send end_stream on the header frame it sends
• Consume the response, then assert the goaway