update github actions to use node.js 20

[jenshu]

Currently regression tests in CI show warnings like this:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, styfle/[email protected], actions/setup-go@v4, actions/cache@v3, helm/[email protected], azure/setup-kubectl@v3, azure/setup-helm@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

from the above link:

Our plan is to transition all actions to run on Node 20 by Spring 2024

Some of the actions we are using don't have a version that uses node 20 yet, but when they are available we should upgrade.