loader: fix --inspect-brk

PR-URL: https://github.com/nodejs/node/pull/18949
Fixes: https://github.com/nodejs/node/issues/18948


Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Guy Bedford <guybedford@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: James M Snell <jasnell@gmail.com>