HTTP/1.1 connection reuse returns unsolicited server data as the next request's response (regression in 8.22.0)

Since 8.22.0 libcurl reuses an idle HTTP/1.1 connection that already has unread bytes waiting on it, as long as the pool health check ran less than a second ago, and those bytes are then returned as the response to the next request sent on that connection, so every later response on it is shifted …