A mirror of a github repository is setup and contains two remotes:
gitlab git@workbench.dachary.org:tests/testrepo.git (push) origin https://github.com/loic-bot/testrepo (push)
The github2gitlab command of gh (run from ~gitmirrors/repositories/Tests/testrepo) creates a merge request in gitlab by copying the designated pull request from github:
$ gh gg --user loic-bot --repo testrepo --number 3