Make GitHub login possible for existing accounts ("Email has already been taken")

1. I registered on GitLab.com with my e-mail address and completed the registration
2. Then I tried to login using GitHub, since that's a bit easier for me. I was thinking it would automatically connect to my GitLab account, based on the e-mail address. However, this is not the case, and I got "Email has already been taken" in the URL: https://gitlab.com/users/auth/github/omniauth_error?error=Email+has+already+been+taken

This is a request to automatically map login requests "Email has already been taken" to an existing account (provided you log in into your existing GitLab account once to actually do the merge).