Clarification needed on auth for REST API Actions artefact endpoints

[danielhardej]

Currently, the docs for the Download an artifact REST endpoint state that:

This endpoint can be used without authentication or the aforementioned permissions if only public resources are requested.

This section of the docs appears to be outdated in this case. One can download artefacts and logs without authorisation, but one must have authentication, i.e. the user must be logged in.

All this would need is a small update to state:

This endpoint can be used without explicit authorisation or the aforementioned permissions if only public resources are requested; however, authentication is still required to be able to use this endpoint i.e. the user must be logged in, or be using a valid token.

This would resolve the concerns raised in:

github/docs#36482
/~https://github.com/github/c2c-actions-support/issues/4044

cc @subatoi