building iso doesn't respect rootfs parameter

[mbarak]

When trying to build an ISO the --rootfs parameter is ignored.

An invocation with --rootfs btrfs and --type iso such as:

    sudo podman run \
      --rm \
      -it \
      --privileged \
      --pull=newer \
      --net=host \
      --security-opt label=type:unconfined_t \
      -v ./config.toml:/config.toml:ro \
      -v ./output:/output \
      -v /var/lib/containers/storage:/var/lib/containers/storage \
      "quay.io/centos-bootc/bootc-image-builder:latest" \
      --use-librepo=True \
      --rootfs btrfs \
      --type iso \
      --chown $UID:$UID \
      "{{ target_image }}:{{ tag }}"

and with config.toml that only defines a user to add such as:

[[customizations.user]]
name = "user"
password = "password"
key = "sshkey"
groups = ["wheel"]

Will produce an ISO with an anaconda/kickstarter script that hard codes ext4 as the filesystem format. osbuild.ks in the ISO contains:

part / --fstype=ext4 --grow

and the resulting ISO installer will partition the disk with ext4, ignoring the chosen --rootfs

bib version:

> sudo podman run --rm -it quay.io/centos-bootc/bootc-image-builder:latest version
build_revision: 94fb1c5
build_time: 2025-05-12T07:46:51Z
build_tainted: true