如何修复这些 APT 存储库错误？我正在使用 Debian GNU/Linux 9.13（延伸）。我正在修复此更新错误并导入 Docker GPG 密钥。
root@test:~# apt-get update
Ign:1 http://security.debian.org stretch/updates InRelease
Err:2 http://security.debian.org stretch/updates Release
404 Not Found [IP: 111.73.1113.145 90]
Get:3 https://download.docker.com/linux/debian stretch InRelease [44.8 kB]
Ign:4 http://ftp.de.debian.org/debian stretch InRelease
Err:5 http://ftp.de.debian.org/debian stretch Release
404 Not Found
Err:3 https://download.docker.com/linux/debian stretch InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7PB0A8C2F192FFDM
Reading package lists... Done
E: The repository 'http://security.debian.org stretch/updates Release' does no longer have a Release file.
N: …