你缺少科学上网的配置？ssh -vvv -T git@github.com 看看。

git 没有账号的概念。

你这是不同的 ssh key，同一个 GitHub 账号。

所有 GitHub 用户都共享一个名叫 git 的 ssh 账号。

根据 ssh 调试信息，考虑防火墙（或者类似的网络限制）的问题。检查 Windows 防火墙设置、网络设置（你的网络是不是不允许访问 22 端口什么的？有没有透明代理？）、最后检查中国特色的部分。

首先上图

➜ .ssh ssh -vvv -T git@github.com

OpenSSH_7.3p1, OpenSSL 1.0.2j  26 Sep 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug2: resolving "github.com" port 22
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to github.com [192.30.253.112] port 22.
debug1: Connection established.
debug1: identity file /home/mugbya/.ssh/id_rsa type 1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/mugbya/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.3
debug1: Remote protocol version 2.0, remote software version libssh-0.7.0
debug1: no match: libssh-0.7.0
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to github.com:22 as 'git'

试了一下不太是ssh证书的问题，你继续排查吧