ci: Don't pass token when downloading assets package

What does this MR do and why?

We always download from the canonical public project so there's no need to pass a token in that case. This will allow other instances to download from the canonical instance/project.

Related to gitlab-com/gl-infra/production#8178 (closed).

The assets package download still works in this MR, so that means the token wasn't needed. 🎉

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