Warnings about various deprecated actions

[amcdavid]

As of 12 June 2023, we are getting warnings about Node 12 deprecation in the following:

• r-build-and-check actions/checkout@v2, actions/cache@v1
• docker-build-and-push actions/checkout@v2, docker/setup-buildx-action@79abd3f

We are getting warnings about save-state or set-output in docker-build-and-push. See this run, for instance.

It looks like fixes for all of these might just involve bumping the actions version, as I don't see any calls to the deprecated APIs directly in the workflow. I may take a crack at fixing this when I get a couple hours to play around.

[LiNk-NY]

This should be fixed in #40. Let us know if you spot anything else. Thank you! @amcdavid