Node 20 upgrade

[palfrey]

I'm now seeing the error in my logs

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: pat-s/[email protected]. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

See also https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/ but basically, this needs upgrading