GitLab docs explicitly say `needs` does not require stages but GitLab actual behavior is:

```
Found errors in your .gitlab-ci.yml:

    update-staging job needs system-tests job, but system-tests is not in any previous stage
    update-staging job needs morph-build-staging job, but morph-build-staging is not in any previous stage

```

Automate updating nixpkgs pin in develop branch once a week

See merge request !305

The default is `when: "on_success"` which is equivalent to "always" since we
have no stages.

Some terminal code stripping logic added though

except it is probably not set in this env for some dumb reason

Previous CI runs created TARGET_BRANCH and updated it but failed to push.  But
the branch still exists in the CI environment, with the changes!  Hooray.
Mutable shit!