loginctl doesn't output json

Seems like the exact flag changed in recent systemd versions  

Related:
https://github.com/kolide/launcher/issues/1758
https://github.com/systemd/systemd/issues/15275
https://github.com/systemd/systemd/pull/16176

_Originally posted by @omertuc in https://github.com/containers/bootc/pull/1063#discussion_r1946311541_
            