trivial: case insensitive while explorering cabinet files
trivial: case insensitive while explorering cabinet files

The cabinet file's extension name disregards uppercase or lowercase

fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd