Debian 8禁用软件包有效性校验后仍出现认证警告的问题求助

各位好，我遇到了一个头疼的问题，想请教下大家：

我现在在老旧的Banana Pi BPI-R1硬件上跑着Debian 8 "Jessie"，最近安装软件包的时候总是弹出这个警告：

WARNING: The following packages cannot be authenticated!

我先执行了apt update，输出如下：

Ign http://archive.debian.org jessie InRelease
Get:1 http://archive.debian.org jessie-backports InRelease [166 kB]
...
Hit http://archive.debian.org jessie/contrib armhf Packages
Fetched 168 kB in 26s (6457 B/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
34 packages can be upgraded. Run 'apt list --upgradable' to see them.

W: GPG error: http://archive.debian.org jessie-backports InRelease: The following signatures were invalid: KEYEXPIRED 1587841717 KEYEXPIRED 1668891673
W: GPG error: http://archive.debian.org jessie Release: The following signatures were invalid: KEYEXPIRED 1587841717

能看出来是Debian的GPG密钥在2022年过期了。我搜索后找到了一个禁用有效性校验的解决方案，按照步骤操作后，我验证了设置确实生效了：

$ apt-config dump|grep Valid
Acquire::Check-Valid-Until "false";

但问题依旧存在！比如我尝试安装dpkg-sig的时候，还是会出现认证失败的提示：

Reading package lists... Done
Building dependency tree
Reading state information... Done
...
Install these packages without verification? [y/N]
E: Some packages could not be authenticated

有没有大佬能指点下我哪里操作错了？目前我还没打算更换硬件或者升级到新版本的Debian... 😅

备注：内容来源于stack exchange，提问作者user7440925