PPC ISOs are always taken as "non bootable"
osinfo_media_create_from_location() always returns that a PPC ISO is non bootable. The reason why it occurs is because PPC doesn't rely on El Torito headers but, instead, checks whether the "/ppc/bootinfo.txt" file exists.
Ideally, libosinfo should do something similar to isoinfo -J -i ppc_media.iso -f
in order to check for the "/ppc/bootinfo.txt".