ci: update Node.js actions to 24 and test matrix to [20, 24]

[kentkwu]

What's Changed

Node.js 20 LTS reaches end-of-life on April 30, 2026.

This PR updates Node.js usage in CI to 24, and updates the test matrix for node to [20, 24].

This ensures we test the current active LTS (24) and oldest maintenance LTS (20).

See: https://nodejs.org/en/about/previous-releases#release-schedule

Closes #410

[kou]

This does not change the required engine in package.json. It is only a CI change

Does this mean that we keep supporting Node.js 20? If so, is it OK that we don't use Node.js 20 in our CI?

@trxcllnt @domoritz Do you have any concern that we require Node.js 24 or later?

[Copilot]

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[kentkwu]

@kou, the library requirements are still the same. So this change is not dropping support for 20. This is handled via package.json

  "engines": {
    "node": ">=20.0"
  },

However, the concern about dropping 20 in CI for tests is valid. I updated to matrix [20, 24] so we can test against current active LTS (24) and oldest maintenance LTS (20). Let me know if there are any objections.

[domoritz]

No concerns about keeping up to date with new node versions.

[kou]

+1

Could you update the PR title and description?