test: escape script filename on Windows

Escape backslashes in script filename on Windows in a CLI test.

PR-URL: https://github.com/nodejs/node/pull/16124
Fixes: https://github.com/nodejs/node/issues/16057

 and #16023
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: James M Snell <jasnell@gmail.com>