Update action to node 20

[romnn]

Hi!

Thanks for your great GitHub action! I really enjoy using it!

I am seeing the same warning as mentioned in #311 since actions require node 20 now (see https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/)

Simply changing the node version in action.yml should resolve this.

Best, Roman