Fix a typo in a rt::io::signal test

It was pretty much a miracle that these tests were ever passing. They would
never have passed in the single threaded case because only one sigint in the
tests is ever generated, but when run in parallel two sigints will be generated.
Ignore a test which never completes on windows

I'm not entirely sure why this is happening, but the server task is never seeing
the second send of the client task, and this test will very reliably fail to
complete on windows.
auto merge of #10098 : alexcrichton/rust/attempts, r=alexcrichton

It was pretty much a miracle that these tests were ever passing. They would
never have passed in the single threaded case because only one sigint in the
tests is ever generated, but when run in parallel two sigints will be generated.