update node in github workflow

[ineiti]

github workflow complains that we're using node 12, which is deprecated. We should update to node 16, or check if it runs with a later node.

[PascalinDe]

https://github.com/search?q=repo%3Ac4dt%2Fd-voting+path%3A%2F%5E%5C.github%5C%2Fworkflows%5C%2F%2F+node&type=code shows me node 16-18, can this ticket be closed?

[ineiti]

In the meantime, node 16 is also too old, and everything runs on node 20:

The following actions use a deprecated Node.js version and will be forced to run on node20: actions/setup-go@v4, actions/checkout@v3. For more info: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/

Probably it's enough to update the @... in the .github/workflows files.