ci(deps): update GitHub actions to run on Node.js 24 (LTS)

[MikeMcC399]

Situation

• GitHub has deprecated the use of node20 and plans to force runners to use node24 beginning on Mar 4, 2026 - see Deprecation of Node 20 on GitHub Actions runners.

• Node.js 20 is planned for end-of-life on April 30, 2026.

• .nvmrc defines Node.js 20 for usage

GitHub Actions workflows are currently based on node20 versions

• main.yml
• publish-on-tag.yml

Change

Update

• .nvmrc to Node.js 24 Active LTS version

Update the above GitHub Actions workflows to use latest node24 versions:

• actions/checkout to actions/checkout@v6
• actions/setup-node to actions/setup-node@v6

[MikeMcC399]

@mathiasbynens

Would you like to review? It just puts CI on a current basis.