Update action runtime to Node.js 24 (Node.js 20 deprecation)

[123yoshidandy]

GitHub Actions is deprecating Node.js 20 as a JavaScript action runtime. According to the official announcement:

• 2026-06-02: Node.js 24 becomes the default; Node.js 20 actions need an opt-in env var to keep running.
• 2026-09-16: Node.js 20 is removed from runners entirely.

Reference: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Since this action declares using: 'node20' in action.yml, workflows that consume it currently emit the following warning:

Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: Legion2/swagger-ui-action@... .
Actions will be forced to run with Node.js 24 by default starting June 2nd, 2026. Node.js 20 will be removed from the runner on September 16th, 2026.

In the same spirit as #481 (the Node.js 16 → 20 bump), would you be open to a PR upgrading the runtime to Node.js 24? I'm happy to prepare it. The proposed changes would be:

• action.yml: using: 'node20' → using: 'node24'
• package.json: align engines.node with Node 24, bump @types/node to a v24-compatible release
• Regenerate package-lock.json
• Run npm run all and commit the rebuilt dist/

Please let me know if you'd like me to proceed.