Update to Node.js 24

[rowanfr]

Node.js 20 actions are deprecated. bufbuild/buf-setup-action should be updates to node version to 24. Warnings have also started to appear in workflow annotations.

[emcfarlane]

Hey @rowanfr, this action has been deprecated in favour of the unified buf-action. If you are able to migrate to the new action please check out the migration guide. Let me know if you have any issues.

[rowanfr]

Thanks for the clarification. I'll migrate over.