Comment 3 for bug 2031943

Same as above John's comment.
Tested proposed livecd-rootfs with Realtime image AWS which kernel version is 5.15

1. Building image with `ubuntu-bartender` from `ubuntu-old-fashioned`
    1a. project=ubuntu-cpc image-target=ec2-pro-realtime

2. Log file check
+ snap_validate_seed /tmp/tmp.ymGEaZ1Bbc
+ local CHROOT_ROOT=/tmp/tmp.ymGEaZ1Bbc
+ '[' -e /tmp/tmp.ymGEaZ1Bbc/boot/vmlinuz ']'
++ readlink --canonicalize --no-newline /tmp/tmp.ymGEaZ1Bbc/boot/vmlinuz
++ grep --extended-regexp --only-matching --max-count 1 '[0-9]+\.[0-9]+'
+ local kern_major_min=5.15
+ '[' -d /usr/share/livecd-rootfs/live-build/apparmor/5.15 ']'
+ '[' -e /tmp/tmp.ymGEaZ1Bbc/var/lib/snapd/seed/seed.yaml ']'
+ snap debug validate-seed /tmp/tmp.ymGEaZ1Bbc/var/lib/snapd/seed/seed.yaml
++ realpath /tmp/tmp.ymGEaZ1Bbc
+ /usr/lib/snapd/snap-preseed --reset /tmp/tmp.ymGEaZ1Bbc
++ realpath /tmp/tmp.ymGEaZ1Bbc
+ /usr/lib/snapd/snap-preseed /tmp/tmp.ymGEaZ1Bbc
ubuntu classic preseeding
starting to preseed root: /tmp/tmp.ymGEaZ1Bbc
using snapd binary: /tmp/snapd-preseed/usr/lib/snapd/snapd (2.59.5)
2023/08/22 13:36:56.513867 main.go:57: running for preseeding
2023/08/22 13:36:56.541899 overlord.go:272: Acquiring state lock file
2023/08/22 13:36:56.541919 overlord.go:277: Acquired state lock file
2023/08/22 13:36:56.594654 daemon.go:247: started snapd/2.59.5 (series 16; classic) ubuntu/22.04 (amd64) linux/5.15.0-1041-aws.
2023/08/22 13:36:56.610803 daemon.go:340: adjusting startup timeout by 30s (pessimistic estimate of 30s plus 5s per snap)
2023/08/22 13:36:56.624055 backends.go:58: AppArmor status: apparmor is enabled and all features are available
2023/08/22 13:36:57.153210 helpers.go:146: error trying to compare the snap system key: system-key missing on disk
2023/08/22 13:37:06.764204 daemon.go:428: stopping snapd as requested
2023/08/22 13:37:06.779818 daemon.go:521: gracefully waiting for running hooks
2023/08/22 13:37:06.779836 daemon.go:523: done waiting for running hooks
2023/08/22 13:37:06.780356 overlord.go:516: Released state lock file
unmounting: /tmp/snapd-preseed

3. register image and check kernel&snap debug seeding result

ubuntu@ip-172-31-26-219:~$ snap debug seeding
seeded: true
preseeded: true
image-preseeding: 8.3s
seed-completion: 3720h29m46.734s
ubuntu@ip-172-31-26-219:~$ uname -a
Linux ip-172-31-26-219 5.15.0-1043-realtime #48-Ubuntu SMP PREEMPT_RT Thu Jul 13 20:54:21 UTC 2023 aarch64 aarch64 aarch64 GNU/Linux

This verification shows snap seeds are validated with correct kernel version