libvirt: use /run for runstatedir

systemd complains:

	Jul 08 12:43:59 kaiser systemd[1]: /nix/store/bvfikb8v9m646m23fqm0rfnnsj6plc2k-libvirt-6.2.0/lib/systemd/system/libvirtd-admin.socket:11: ListenStream= references a path below legacy directory /var/run/, updating /var/run/libvirt/libvirt-admin-sock → /run/libvirt/libvirt-admin-sock; please update the unit file accordingly.
	Jul 08 12:43:59 kaiser systemd[1]: /nix/store/bvfikb8v9m646m23fqm0rfnnsj6plc2k-libvirt-6.2.0/lib/systemd/system/libvirtd-ro.socket:11: ListenStream= references a path below legacy directory /var/run/, updating /var/run/libvirt/libvirt-sock-ro → /run/libvirt/libvirt-sock-ro; please update the unit file accordingly.
	Jul 08 12:43:59 kaiser systemd[1]: /nix/store/bvfikb8v9m646m23fqm0rfnnsj6plc2k-libvirt-6.2.0/lib/systemd/system/libvirtd.socket:9: ListenStream= references a path below legacy directory /var/run/, updating /var/run/libvirt/libvirt-sock → /run/libvirt/libvirt-sock; please update the unit file accordingly.

Let's just set it correctly manually, that is what Red Hat does:

https://gitlab.com/libvirt/libvirt/-/commit/ba7592f6c17d50435582e597727fbfc51322d606

See also:

https://gitlab.com/libvirt/libvirt/-/commit/390997925a3aca1b57969526c3e083761fafe7c3