Update to Node24

Two of our actions don't have Node 24 releases yet, so we're still seeing this deprecation warning on every build:

> Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: `peaceiris/actions-hugo@v2`, `cloudflare/wrangler-action@v3`. 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.

Already on Node 24:

- [x] `actions/checkout@v5`
- [x] `peter-evans/create-pull-request@v8`

Still waiting on upstream:

- [ ] `peaceiris/actions-hugo` — https://github.com/peaceiris/actions-hugo/issues/675
- [ ] `cloudflare/wrangler-action` — https://github.com/cloudflare/wrangler-action/issues/413

Once both are released we can bump the versions and close this. The hard deadline is June 2nd 2026 — after that GitHub forces Node 24 by default. If we hit June 2 and either of these still isn't released, we can fall back to setting `FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true` in the workflow as a temporary measure.