Copying of stdout/stderr causes frequent deadlocks under WSL2

[istyf]

Running the unit tests have a near (if not) 100% reproducible deadlock between all of the different output writers, caused by contention of a semaphore deep in the posix file system to be able to output text.

I have not had the time to root out the exact reason, but the use of io.Copy(os.Stdout, stdout) seems to be the culprit, because if that is changed the deadlock is no longer reproducible.

It seems reasonable that this deadlock could also happen within air itself and not only in the unit tests.