Harden stream processing close test

[kanongil]

I fixed the test to be compatible with node 16, which allows the req to be closed while the connection itself is still active.

I also revised the stream, so we can really validate that the processing is stopped.

This is in response to #4262 (comment).

[devinivy]

That feels much better.

One thing I want to gut-check with you: do you believe that this test simulated bad/unexpected behavior from node's http server, and in turn it's not something critical to cover in node v14 and below? I see that this test has existed since the very early days of the framework, so perhaps it was more important when node was less stable/mature.

[kanongil]

As I see it, the test validates that streams stop being processed when a request stops due to downstream / internal issues. My patch updates it so that it better does this with v16 (emitting close on req can no longer be used for this).

Seem legit, but might be tested by some other case. Removing it does not change coverage.