Update CI workflow

[surilindur]

This is a small set of changes to bump the actions versions, and to add better names to some of the steps:

• Run tests on Node 22 instead of 21 (in addition to 18 and 20).
• Cache the .yarn folder because that is the main one needed for Yarn version 4.
• Wait for linting to finish before running unit tests. The CI is so short that this makes sense. If the CI is too slow, it is because Jest is running with too many workers, which will be fixed in another PR.
• Ensure the Coveralls coverage is supplied the correct key, to avoid false duplicates in the report.
• Cancel in-progress workflows when new commits are pushed to a branch.
• Use the --immutable flag to detect any lockfile inconsistencies in the CI.

[rubensworks]

Why not cache node_modules anymore?

[surilindur]

Because the linking step (to unpack the downloaded packages into node_modules) is faster than the download step, so it is more efficient to cache the download cache of Yarn (located in .yarn). That way, Yarn can skip the download step, which is most expensive, and proceed to just comparing its local cache against the server versions, and then do unpacking.

[rubensworks]

But if we just cache node_modules, we don't have to 1) download, and 2) link. So it's more efficient to cache that, right?

[surilindur]

I changed it back to caching node_modules instead.

[rubensworks]

Thanks!