docker - sudo apt-get update でストレッチ リリースの Docker パッケージが見つからない

Question

チュートリアルに従ってリポジトリを追加しましたhttps://docs.docker.com/install/linux/docker-ce/ubuntu/#install-using-the-repository

しかし、sudo apt-get update を実行すると、次のスタックが得られます

Ign:9 https://download.docker.com/linux/ubuntu stretch/stable amd64 Packages
Ign:10 https://download.docker.com/linux/ubuntu stretch/stable all Packages
Ign:12 https://download.docker.com/linux/ubuntu stretch/stable Translation-en
Ign:13 https://download.docker.com/linux/ubuntu stretch/stable Translation-en_US
Err:9 https://download.docker.com/linux/ubuntu stretch/stable amd64 Packages
  404  Not Found
Ign:10 https://download.docker.com/linux/ubuntu stretch/stable all Packages
Ign:12 https://download.docker.com/linux/ubuntu stretch/stable Translation-en
Ign:13 https://download.docker.com/linux/ubuntu stretch/stable Translation-en_US
Reading package lists... Done
W: The repository 'https://download.docker.com/linux/ubuntu stretch Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch https://download.docker.com/linux/ubuntu/dists/stretch/stable/binary-amd64/Packages  404  Not Found`

私の /etc/apt/sources.list は次のとおりです

deb http://deb.debian.org/debian stretch main
deb http://security.debian.org/debian-security stretch/updates main
deb [arch=amd64] https://download.docker.com/linux/ubuntu stretch stable
# deb-src [arch=amd64] https://download.docker.com/linux/ubuntu stretch stable