我收到一个弹出窗口，询问我输入的 gitlab 用户名和密码，但失败了.

I get a popup asking for my gitlab username and password which I enter and which fails.

检查，如评论:

• git remote -v
• git config credential.helper

如果第一个以 https:// 开头，并且第二个不为空，则您看到的是一个 Git 凭据帮助程序，它试图缓存您的 HTTPS 凭据.
这意味着您的 SSH 密钥无论如何都会被忽略.

If the first starts with https://, and the second is not empty, what you see is a Git credential helper trying to cache your HTTPS credentials.
That means your SSH key would be ignored anyway.

关于错误消息，请查看此线程，以及测试它:

Regarding the error message, check out this thread, and test it with:

ssh -o UpdateHostKeys=no -Tv git@gitlab.com

为了使其持久化，在~/.ssh/config中:

To make it persistent, in ~/.ssh/config:

Host gitlab.com
  UpdateHostKeys no