Description of my issue
This morning I tried to update my system, but it seems, that one repository is not available or broken. it says, there is no release file.
# apt update
Hit:1 http://security.debian.org/debian-security stretch/updates InRelease
Ign:2 http://ftp.de.debian.org/debian stretch InRelease
Hit:3 http://ftp.de.debian.org/debian stretch-updates InRelease
Hit:4 http://ftp.de.debian.org/debian stretch Release
Hit:5 https://packages.sury.org/php stretch InRelease
Ign:7 http://forge.yunohost.org/debian stretch InRelease
Err:8 http://forge.yunohost.org/debian stretch Release
Unable to connect to forge.yunohost.org:http: [IP: 2a03:7220:8080:5c00::1 80]
Reading package lists... Done
E: The repository 'http://forge.yunohost.org/debian stretch Release' does no longer have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.