VM image: check the factory snapshot holds no SSH login key

The install test's key sits in the user's home, which is its own
subvolume and not part of the factory snapshot, and the seal removes it
there. The check says so of every image, instead of leaving it to the
layout staying as it is.

test/vm-image/vm-verify

@@ -41,6 +41,7 @@ check "no shell history" sh -c '! [ -e ~/.bash_history ]'
 check "the package cache is empty" [ -z "$(ls /var/cache/pacman/pkg)" ]
 root mkdir -p /run/top && root mount -o subvolid=5,ro "$(findmnt -no SOURCE / | sed 's/\[.*//')" /run/top
 check "the factory snapshot has no machine ID" sh -c "! printf '%s\n' '$PW' | sudo -S -p '' test -s /run/top/@factory/etc/machine-id"
+check "the factory snapshot holds no SSH login key" sh -c "! printf '%s\n' '$PW' | sudo -S -p '' sh -c 'ls /run/top/@factory/root/.ssh/authorized_keys /run/top/@factory/home/*/.ssh/authorized_keys' 2>/dev/null | grep -q ."
 check "the factory snapshot has no SSH host keys" sh -c "[ -z \"\$(printf '%s\n' '$PW' | sudo -S -p '' sh -c 'ls /run/top/@factory/etc/ssh/ssh_host_* 2>/dev/null')\" ]"
 check "no snapshots besides the current system" [ -z "$(root ls /.snapshots)" ]
 echo "omarchy $(pacman -Q omarchy 2>/dev/null | cut -d' ' -f2), kernel $(uname -r), $(systemd-analyze | head -1)"