autoinstall.yaml - resize partition fails bc it doesn't unmount

I'm just trying to resize partitions during install for a dual-boot scenario.

Bug report details: https://bugs.launchpad.net/subiquity/+bug/2068803

here is the yaml:

#cloud-config
autoinstall:
  version: 1
  interactive-sections:
    - network
  identity:
    hostname: sdm3
    password: pw
    realname: sdm
    username: sdm
  keyboard:
    layout: us
  locale: en_US.UTF-8
  ssh:
    allow-pw: true
    authorized-keys: []
    install-server: false
  storage:
    config:
    - transport: pcie
      preserve: true
      id: nvme-controller-nvme0
      type: nvme_controller
    - ptable: gpt
      path: /dev/nvme0n1
      preserve: true
      grub_device: false
      id: disk-nvme0n1
      type: disk
    - device: disk-nvme0n1
      size: 104857600
      flag: boot
      number: 1
      preserve: true
      grub_device: true
      path: /dev/nvme0n1p1
      id: partition-nvme0n1p1
      type: partition
    - device: disk-nvme0n1
      size: 16777216
      flag: msftres
      number: 2
      preserve: true
      grub_device: false
      path: /dev/nvme0n1p2
      id: partition-nvme0n1p2
      type: partition
    - device: disk-nvme0n1
      size: 817889280
      number: 3
      preserve: true
      grub_device: false
      path: /dev/nvme0n1p3
      id: partition-nvme0n1p3
      type: partition
    - device: disk-nvme0n1
      size: 460504170496
      number: 4
      preserve: true
      grub_device: false
      resize: true
      path: /dev/nvme0n1p4
      id: partition-nvme0n1p4
      type: partition
    - device: disk-nvme0n1
      size: -1
      wipe: superblock
      number: 5
      preserve: false
      id: partition-0
      type: partition
    - fstype: ext4
      volume: partition-0
      preserve: false
      id: format-0
      type: format
    - path: /
      device: format-0
      id: mount-1
      type: mount
    - fstype: vfat
      volume: partition-nvme0n1p1
      preserve: true
      id: format-partition-nvme0n1p1
      type: format
    - path: /boot/efi
      device: format-partition-nvme0n1p1
      id: mount-0
      type: mount
  timezone: America/New_York