Update workflow github actions to node-20

[Alenar]

Why

In our github actions pipelines there's warnings asking us to update our workflows:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/setup-node@v3, actions/upload-artifact@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

You can see them popping in the last merge on main: https://github.com/input-output-hk/mithril/actions/runs/8002289789

What

Since Node 16 have reached end of life in October 2023, github actions are switching to node20 as the new default.

How

We need to check that the actions that we use have been updated, if their maintainers plans to do so, else if there's alternative or ... do nothing as they may not been running on node 20 but their code doesn't use api that have changes (meaning that github will continue to output unpleasant warnings in our pipelines).

[Alenar]

Done with PR #1521