h2: If we send a GOAWAY, we shouldn't be surprised at a connection reset

[fasterthanlime]

Describe the bug

Not really a bug but see this log, that's the end of http2/5.1.2:

 WARN fluke::h2::server: connection error: max concurrent streams exceeded (more than 32) (MaxConcurrentStreamsExceeded { max_concurrent_streams: 32 }) (code ProtocolError)
DEBUG fluke::h2::server: Sending GoAway last_stream_id=65 error_code=ProtocolError
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 29, payload: BodyChunk }
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 63, payload: Headers }
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 31, payload: BodyChunk }
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
        ✔ 1: Sends HEADERS frames that causes their advertised concurrent stream limit to be exceeded
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 33, payload: BodyChunk }

Finished in 0.0596 seconds
1 tests, 1 passed, 0 skipped, 0 failed
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 35, payload: BodyChunk }
DEBUG fluke::h2::server: Handler completed successfully, gave us a responder
DEBUG fluke::h2::server: Writing ev=H2Event { stream_id: 37, payload: BodyChunk }
DEBUG fluke::h2::server: caught error from one of the tasks: read error: read_into for read_and_parse::<fluke::h2::parse::Frame> / Read(
    Error {
        msg: "read_into for read_and_parse::<fluke::h2::parse::Frame>",
        source: Os {
            code: 104,
            kind: ConnectionReset,
            message: "Connection reset by peer",
        },
    },
)
ERROR fluke_h2spec: error serving client 127.0.0.1:60488: read error: read_into for read_and_parse::<fluke::h2::parse::Frame>
DEBUG fluke::h2::server: Handler returned an error: could not send event to h2 connection handler
DEBUG fluke::h2::server: Handler returned an error: could not send event to h2 connection handler
 WARN fluke::h2::encode: could not send event to h2 connection handler
 WARN fluke::h2::encode: could not send event to h2 connection handler

Expected behavior

If we've sent a GOAWAY, we should fully expect to 1) not be able to write further messages, 2) get a connection reset when we try to read more messages.

This can probably be done by just having a "has_sent_goaway" flag somewhere.