…on#139610)Fix a flaky test introduced in13dc2fd.After a single HTTP/0.9 request, both client and server are expected toclose the connection on their side. In particular, if a client sends tworequests with the same connection, only the first one should be handled.In the tests, it might happen that checking for the second request to beignored did not take into account that the server may have already closedthe connection. This flaky behavior was first observed on macOS CI workersbut could not be reproduced locally on a Linux machine.