This is created in GitLab and should mirror over to GitHub via ssh easily. edit: It does, yay!
Push mirroring is setup on the GitLab side, targeting ssh://[email protected]/TheKolega/mirror-test-github.git and using SSH auth.
This creates an public SSH key which can pe copied over to GitHub either as a global SSH key for that user or a deployment key on a specific repo.
Optionally, fine-grained PATs can also be used with the Password authentication method.