系统环境：FydeOS v8.21 全新安装，启用的 Linux 和 Android 子系统均能正常使用（Linux 中 VSCode+miniconda3 可运行，Android 可打开设置）
问题：在 Linux 子系统中尝试刷新软件源列表时出现签名错误，无法继续更新
$ sudo apt update
忽略:1 http://mirrors.aliyun.com/debian stretch InRelease
命中:2 http://mirrors.aliyun.com/debian-security stretch/updates InRelease
命中:3 http://mirrors.aliyun.com/debian stretch Release
命中:4 http://packages.microsoft.com/repos/vscode stable InRelease
命中:6 https://apt.llvm.org/stretch llvm-toolchain-stretch-7 InRelease
忽略:7 https://deb-mirror.fydeos.com/cros-packages/77 stretch InRelease
获取:8 https://deb-mirror.fydeos.com/cros-packages/77 stretch Release [3,114 B]
获取:9 https://deb-mirror.fydeos.com/cros-packages/77 stretch Release.gpg [819 B]
忽略:9 https://deb-mirror.fydeos.com/cros-packages/77 stretch Release.gpg
忽略:10 https://mirrors.tuna.tsinghua.edu.cn/debian stretch InRelease
获取:11 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-updates InRelease [91.0 kB]
获取:12 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports InRelease [91.8 kB]
命中:13 https://deb.debian.org/debian stretch-backports InRelease
获取:14 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates InRelease [94.3 kB]
获取:15 https://mirrors.tuna.tsinghua.edu.cn/debian stretch Release [118 kB]
获取:16 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-updates/main amd64 Packages [27.9 kB]
获取:17 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-updates/main Translation-en [11.9 kB]
获取:18 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/main amd64 Packages [607 kB]
获取:19 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/main Translation-en [464 kB]
获取:20 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/contrib amd64 Packages [10.9 kB]
获取:21 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/contrib Translation-en [7,237 B]
获取:22 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/non-free amd64 Packages [33.0 kB]
获取:23 https://mirrors.tuna.tsinghua.edu.cn/debian stretch-backports/non-free Translation-en [38.2 kB]
获取:24 https://mirrors.tuna.tsinghua.edu.cn/debian stretch Release.gpg [2,410 B]
获取:25 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/main amd64 Packages [520 kB]
获取:26 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/main Translation-en [230 kB]
获取:27 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/contrib amd64 Packages [1,760 B]
获取:28 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/contrib Translation-en [1,759 B]
获取:29 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/non-free amd64 Packages [1,596 B]
获取:30 https://mirrors.tuna.tsinghua.edu.cn/debian-security stretch/updates/non-free Translation-en [691 B]
获取:31 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main amd64 Packages [7,083 kB]
获取:32 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main Translation-en [5,381 kB]
获取:33 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main Translation-zh_CN [96.3 kB]
获取:34 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/main Translation-zh [1,526 B]
获取:35 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/contrib amd64 Packages [50.9 kB]
获取:36 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/contrib Translation-en [45.9 kB]
获取:37 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/non-free amd64 Packages [78.4 kB]
获取:38 https://mirrors.tuna.tsinghua.edu.cn/debian stretch/non-free Translation-en [80.3 kB]
正在读取软件包列表... 完成
W: GPG 错误：https://deb-mirror.fydeos.com/cros-packages/77 stretch Release: 下列签名无效： EXPKEYSIG 6494C6D6997C215E Google Inc. (Linux Packages Signing Authority) <linux-packages-keymaster@google.com>
E: 仓库 “https://deb-mirror.fydeos.com/cros-packages/77 stretch Release” 没有数字签名。
N: 无法安全地用该源进行更新，所以默认禁用该源。
N: 参见 apt-secure(8) 手册以了解仓库创建和用户配置方面的细节