regress_http: disable http/read_on_write_error under win32 EVHTTP_CON_READ_ON_WRITE_ERROR works only if an error already read from the socket, but if we already got EPIPE on write we cannot read from the socket anymore, and win32 does not guarantee that read will happens before (although it happens from time to time). In the referenced patch I just replaced callback with not expecting 417, but like I already wrote, this is not always true (i.e. it is flacky). Fixes: 3b581693ac1967f7f8d98491cb772a1b415eb4cd ("test/http: read_on_write_error: fix it for win32")