After installing Debian Testing "Bullseye" mid March 2020 I got an
error trying to run apt update.
2020年3月中旬安装Debian Testing "Bullseye"后，尝试运行 apt update 时出现错误。

E: The repository 'http://security.debian.org./debian-security 
bullseye/updates Release' does not have a Release file.

Unfortunately, the Debian maintainers managed to let a bug creep into
the /etc/apt/sources.list. It’s called "Testing" for a reason, I
guess.
很不幸，Debian的维护者们在 /etc/apt/sources.list 中引入了一个bug。我猜这就是为什么它被称为“测试版”。

The offending lines are this.
这些有问题的行是这样的。

deb http://security.debian.org/debian-security/ bullseye/updates main
deb-src http://security.debian.org/debian-security/ bullseye/updates main

Note "bullseye/updates", which is where the error is. Change those
two lines to look like this.
请注意"bullseye/updates"，这是错误所在。将这两行修改为以下内容。

deb http://security.debian.org/debian-security/ bullseye-security main
deb-src http://security.debian.org/debian-security/ bullseye-security main

After that, the update will work. I have noticed that in a later
version of the installer this bug has been fixed.
之后，更新将会生效。我注意到在安装程序的后续版本中，这个错误已经被修复了。