For what it's worth, I have worked around this issue locally by modifying the
postinst script from systemd-boot to explicitly use the initrd generated by
the dracut script:
/etc/kernel/postinst.d/zz-systemd-boot:
-kernel-install add "$1" "$2"
+kernel-install add "$1" "$2" "${2%/*}/initrd.img-$1"
This is not very nice, but this also happens to bring it in line with the
behaviour of the systemd-boot initramfs post-update hook, which always uses
the three-argument form of kernel-instsll (but it's easier to do there because
the script gets the path of the generated initrd as one of its arguments).
