Fixes e.g.
https://github.com/vercel/next.js/actions/runs/30314671467/job/90137708228#step:12:603
The `native-builder` image (`scripts/native-builder.Dockerfile`), used
by the `build-native` job of `build_and_deploy.yml` to cross-compile
`next-swc`, installed Node.js 20 via the NodeSource setup script. That
script downloads and imports a signing key before configuring the apt
repository. When the key download returns an HTTP 403 from CI runners
the script still exits successfully, so `apt-get install nodejs` falls
back to Ubuntu's stock `nodejs` package, which does **not** bundle
`npm`. The failure only surfaced two layers later when the image ran
`npm i -g @napi-rs/cli` (`npm: not found`, exit 127), breaking the
native build.
This change installs Node.js 20 from the official `nodejs.org` static
tarball instead. The tarball bundles `npm` and `corepack`, is
glibc-linked (matching the previous intent), and does not depend on
NodeSource's apt repository or key server, removing the flaky external
dependency. The install step also asserts `npm --version`, so a future
regression fails at the install layer rather than several layers later.
## test plan
- [x] [full build_and_deploy on this
branch](https://github.com/vercel/next.js/actions/runs/30372888336)
