ci: use Node 24 (ships with npm 11) instead of self-upgrading npm

Node 22 ships with npm 10.x and an in-place 'npm install -g npm@latest'
fails on the GitHub Actions hosted runner with MODULE_NOT_FOUND, even
with --force. Node 24 ships with npm 11 by default, which already
satisfies the >= 11.5.1 requirement for npm Trusted Publishing.