W: GPG error: ftp://ftp.au.debian.org testing InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA NO_PUBKEY 8B48AD6246925553 W: GPG error: ftp://ftp.au.debian.org stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY AED4B06F473041FA