Spurious errors from JLine + test error detection

[mlutze]

https://github.com/mlutze/flix-json/actions/runs/8977911029/job/24657467453#step:5:197

JLine emits a message to stderr when no console is found:

     May 07, 2024 12:53:18 AM org.jline.utils.Log logr
    WARNING: Unable to create a system terminal, creating a dumb terminal (enable debug logging for more information)

flix test considers any output to stderr to be an error.

With their powers combined, these create a race condition where a test fails if the message happens to reach the output stream while the test is running.