解决树莓派更换源之后出错的问题

Reading package lists... Done
W: GPG error: http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian buster InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9165938D90FDDD2E
E: The repository 'http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian buster InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

更换源之后添加公钥即可，执行以下命令：

gpg --keyserver  keyserver.ubuntu.com --recv-keys 9165938D90FDDD2E
gpg --export --armor  9165938D90FDDD2E | sudo apt-key add -