systemd-nspawn does not work without D-Bus anymore since v258

Description:

systemd-nspawn --keep-unit --register=false now fails without running systemd/d-bus daemon:

░ Spawning container 6da79dcad9af-9d30c1683e4c48cf on /.#machine.147e7c53a3aa38ad.
░ Press Ctrl-] three times within 1s to kill container; two times followed by r
░ to reboot container; two times followed by p to poweroff container.
Failed to open system bus: No such file or directory

On v257 it worked. This broke CI pipelines for Arch packages in GitHub Actions for me.

Additional info:

• package version(s): systemd 258-3
• config and/or log files:
• link to upstream bug report, if any: https://github.com/systemd/systemd/issues/39044

I've fixed it in systemd: https://github.com/systemd/systemd/pull/39045, could you backport the fix?

Steps to reproduce:

1. sudo docker run --rm -it --privileged --tmpfs /run ghcr.io/archlinux/archlinux:base-devel
2. pacman -Syu
3. systemd-nspawn --register=false --keep-unit --ephemeral