deb.torproject.org is also served through via an Onion Service: http://sdscoq7snqtznauu.onion/
To use Apt over Tor, the apt transport needs to be installed:
# apt install apt-transport-tor
Then replace the address in the lines added before with, for example:
# For the stable version.
deb tor://sdscoq7snqtznauu.onion/torproject.org <DISTRIBUTION> main
# For the unstable version.
deb tor://sdscoq7snqtznauu.onion/torproject.org tor-nightly-master-<DISTRIBUTION> main
<DISTRIBUTION> with your Operating System codename. Run
lsb_release -c or
cat /etc/debian_version to discover.
Now refresh your sources and try if it's still possible to install tor:
# apt update
# apt install tor