data: switch to images/pxeboot for Fedora unknown
Copy of c9eb52af, but for Fedora 'unknown' instead of 'rawhide'.
Fedora 37 rawhide has dropped syslinux in favour of grub for ISO boot and as such, the 'isolinux/' directory no longer exists. The kernel/initrd files in that directory held 100% identical content to the files in 'images/pxeboot/', so this is a straight swap.
https://bugzilla.redhat.com/show_bug.cgi?id=2103835 Signed-off-by: Daniel P. Berrangé berrange@redhat.com