Worksheet mode is broken under Windows

[smarter]

When clicking "Run worksheet", the spinner appears but no output is ever produced. I suspect #5320 broke it.

[smarter]

/cc @allanrenucci @Duhemm

[Duhemm]

Indeed, the tests in dotty.tools.languageserver.WorksheetTest fail because no output is received. Reverting #5320 fixes the issue.