Release or Release.gpg files may be absent if a new .deb file was uploaded
to apt repository recently. We may need to do a multiple attempts in a loop
to retry downloading of these files.
Needed after 99e9ab67b634a89d0be9eca12c4f1cdc091ee6e8, where I have disabled
looping in termux_download but curl doesn't do retries on 404 error. We
want immediate failure only for 404's on source and build tool URLs.
Leonid Pliushch
Henrik Grimler