CI for private repo repending on private repo on Gitlab

[tkf]

To refresh my memory, I set up a demo that shows the configuration https://gitlab.com/tkfm/gitlabdemodownstream.jl/-/merge_requests/1

Just following https://docs.gitlab.com/ee/ci/ssh_keys/README.html

Concrete steps:

1. Create an SSH key pair with ssh-keygen -t ed25519 -C GitLabDemoDownstream@gitlab-ci -f key
2. Add the public key as a deploy key at https://gitlab.com/tkfm/gitlabdemoupstream.jl/-/settings/repository#js-deploy-keys-settings
3. Add the private key as SSH_PRIVATE_KEY environment variable at https://gitlab.com/tkfm/gitlabdemodownstream.jl/-/settings/ci_cd
   • Turn off Protected switch.
     • Without this, $SSH_PRIVATE_KEY is not set and ssh-add would complain that Error loading key "(stdin)": invalid format Julia 1.5 (#759713949) · Jobs · Takafumi Arakaki / GitLabDemoDownstream.jl · GitLab

— https://gitlab.com/tkfm/gitlabdemodownstream.jl/-/merge_requests/1

The CI for the merge request was run before making these repositories public.

I also invited you to the repositories so that you can see the settings.

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Edit: Protected switch setting would look like: