Kubuntu 22.04 LTS下执行apt更新时Nginx源不支持i386架构及修改源后公钥验证失败的问题求助

大家好，我在Kubuntu 22.04 LTS上执行sudo apt-get update命令更新系统时，碰到了这样的错误提示：

N: Skipping acquire of configured file 'nginx/binary-i386/Packages' as repository 'http://nginx.org/packages/mainline/ubuntu jammy InRelease' doesn't support architecture 'i386'

我自己尝试解决了一下：编辑/etc/apt/sources.list.d目录里的nginx.list文件，把原来的源配置：

deb [signed-by=/usr/share/keyrings/nginx-archive-keyring.gpg] http://nginx.org/packages/mainline/ubuntu jammy nginx

修改成了：

deb [arch=amd64] http://nginx.org/packages/mainline/ubuntu/ bionic nginx

结果这下又出现了新的错误：

The following signatures couldn't be verified because the public key is not available: NO_PUBKEY

有没有大佬能帮我看看怎么解决这个问题呀？

备注：内容来源于stack exchange，提问作者feration48