今天在树莓派上用Dockerfile构建镜像时出现apt无法update的问题

...
 ---> Running in 05393fa6f242
Get:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease [265 kB]
Get:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease [114 kB]
Err:1 http://ports.ubuntu.com/ubuntu-ports focal InRelease
  At least one invalid signature was encountered.
Err:2 http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease
  At least one invalid signature was encountered.
Get:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease [101 kB]
Err:3 http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease
  At least one invalid signature was encountered.
Get:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease [114 kB]
Err:4 http://ports.ubuntu.com/ubuntu-ports focal-security InRelease
  At least one invalid signature was encountered.
Reading package lists...
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal InRelease' is not signed.
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-updates InRelease' is not signed.
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-backports InRelease' is not signed.
W: GPG error: http://ports.ubuntu.com/ubuntu-ports focal-security InRelease: At least one invalid signature was encountered.
E: The repository 'http://ports.ubuntu.com/ubuntu-ports focal-security InRelease' is not signed.
...

解决办法是：
在http://ftp.debian.org/debian/pool/main/libs/libseccomp/下载最新版本的libseccomp2，目前最新版本是：libseccomp2_2.5.1-1_armhf.deb
在树莓派上进行安装

>>> sudo dpkg -i libseccomp2_2.5.1-1_armhf.deb

一切又都正常了

参考：
https://askubuntu.com/a/1264921/685786
https://*.com/a/64463211/7151777