<!--- Please read this! Before opening a new issue, make sure to search for keywords in the issues filtered by the "regression" or "bug" label: - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=regression - https://gitlab.com/gitlab-org/gitlab/issues?label_name%5B%5D=bug and verify the issue you're about to submit isn't a duplicate. ---> ### Summary Push mirroring from GitLab.com to GitHub.com appears to fail with a host key verification error, even when the workflow to configure mirroring is followed correctly. ### Steps to reproduce 1. Create a project on GitLab.com. 1. Create a repository on GitHub.com 1. Configure the GitLab project to [push mirror](https://docs.gitlab.com/ee/user/project/repository/repository_mirroring.html#pushing-to-a-remote-repository-core) itself to the GitHub project via SSH public key authentication. 1. Once configured, copy the provided SSH public key and upload it to GitHub as a deploy key for the repository. 1. Observe that mirroring always fails with the error message below. ### Example Project - [gitlab-gold/ssh-mirror](https://gitlab.com/gitlab-gold/ssh-mirror) ### What is the current *bug* behavior? Push mirroring fails with: ``` 13:close stream to gitaly-ruby: rpc error: code = Unknown desc = Gitlab::Git::RepositoryMirroring::RemoteError: Host key verification failed. fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists. ``` ### What is the expected *correct* behavior? Push mirroring should be configured successfully. ### Relevant logs and/or screenshots  ### Output of checks This bug happens on GitLab.com: 13.0.0-pre b99bef6115f ### Workaround Use https authentication ZD: https://gitlab.zendesk.com/agent/tickets/155896 (GitLab Internal)