Node.js 16 actions are deprecated

[plehegar]

This might be related to #99 .

Using:
[[
- uses: actions/checkout@v4
- uses: w3c/spec-prod@v2
]]
https://github.com/w3c/trace-context/blob/level-2/.github/workflows/auto-publish.yml

generates a warning from the github action:
[[
Build, Validate and Deploy
Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: pnpm/action-setup@v2, 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/.
]]