github workflows should test the Dockerfile

[proppy]

https://github.com/google/xls/pull/1421 fixed the docker build it would be nice to have a way to detect when it's broken again in the future.

ideally there would be a workflow in https://github.com/google/xls/tree/main/.github/workflows that exercise the dockerfile and potentially publish the result under https://github.com/features/packages

[HongshiTan]

Hi, @proppy , if it is not very urgent, I can work on that.