Proper fix for chainloading Windows

I have now been able to reproduce the issue in a VM, it took a while to get Windows installed far enough that it would boot in any shape either from old or new grub.

This bug was fixed in the package grub2-unsigned - 2.12~rc1-10ubuntu2

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grub2-unsigned (2.12~rc1-10ubuntu2) mantic; urgency=medium

  * Merge from Debian unstable to pick up fixes (LP: #2028947); remaining changes:
    - Add Ubuntu sbat data
    - build-efi-images: do not produce -installer.efi.signed. LP: 1863994
    - grub-common: Install canonical-uefi-ca.crt
    - Check signatures
    - Support installing to multiple ESP (LP: 1871821)
    - Disable various bits on i386
    - Split out unsigned artefacts into grub2-unsigned
    - Vcs-Git: Point to ubuntu packaging branch
    - Relax dependencies on grub-common and grub2-common
    - grub-pc: Avoid the possibility of breaking grub on SRU update due
      to ABI change
    - UBUNTU: Default timeout changes
    - Revert "Add jfs module to signed UEFI images. Closes: #950959"
    - Revert "Add f2fs module to signed UEFI images"
    - Install grub-initrd-fallback.service again
    - Build using -O1 on s390x to avoid misoptimization
    - grub-check-signatures: Support gzip compressed kernels (LP: #1954683)
    - grub-multi-install: Reset partition type between partitions (LP: #1997795)
    - Drop i386 from grub-efi-amd64* (LP: #2020907)
    - Turn depends on grub-efi-amd64/arm64 unversioned
    - forward port fix for LP: #1926748
    - Make the grub2/no_efi_extra_removable setting work correctly
    - Forward port the fix for LP: #1930742 and make it conditional (xenial/bionic only)
    - Build grub2-unsigned packages with xz compression
    - Replaced patches:
      - installe-signed.patched
      - grub-install-extra-removable.patch
      - grub-install-removable-shim.patch
    - Added patches:
      + rhboot-f34-dont-use-int-for-efi-status.patch
      + rhboot-f34-make-exit-take-a-return-code.patch
      + suse-grub.texi-add-net_bootp6-document.patch
      + ubuntu-add-devicetree-command-support.patch
      + ubuntu-add-initrd-less-boot-fallback.patch
      + ubuntu-add-initrd-less-boot-messages.patch
      + ubuntu-boot-from-multipath-dependent-symlink.patch
      + ubuntu-dont-verify-loopback-images.patch
      + ubuntu-fix-lzma-decompressor-objcopy.patch
      + ubuntu-grub-install-extra-removable.patch
      + ubuntu-install-signed.patch
      + ubuntu-mkconfig-leave-breadcrumbs.patch
      + ubuntu-os-prober-auto.patch
      + ubuntu-recovery-dis_ucode_ldr.patch
      + ubuntu-resilient-boot-boot-order.patch
      + ubuntu-resilient-boot-ignore-alternative-esps.patch
      + ubuntu-shorter-version-info.patch
      + ubuntu-speed-zsys-history.patch
      + ubuntu-support-initrd-less-boot.patch
      + ubuntu-verifiers-last.patch
      + ubuntu-zfs-enhance-support.patch
      + ubuntu-zfs-gfxpayload-dynamic.patch
      + ubuntu-zfs-gfxpayload-keep-default.patch
      + ubuntu-zfs-insmod-xzio-and-lzopio-on-xen.patch
      + ubuntu-zfs-mkconfig-recovery-title.patch
      + ubuntu-zfs-mkconfig-signed-kernel.patch
      + ubuntu-zfs-mkconfig-ubuntu-distributor.patch
      + ubuntu-zfs-mkconfig-ubuntu-recovery.patch
      + ubuntu-zfs-vt-handoff.patch
  * Dropped Ubuntu changes:
    - Temporarily rmmod peimage for os-prober chainloader entries (LP: #2030810)
  * Revert: "Have -b...