Prevent GitHub workflow from disabling

[jakebeal]

Problems in this repository have appeared without being noticed because the CI was automatically disabled by GitHub after going 60 days without a commit.

This is a known problem, and others have developed solutions for it, e.g.: https://stackoverflow.com/a/78843363/2779147

So we should try setting up the GitHub Workflow Immortality script to address this problem: https://github.com/marketplace/actions/github-workflow-immortality

[jakebeal]

Probably a good place to install the script will be not here, but in https://github.com/SynBioDex/.github , in order to be able to cover all repositories for which we want to keep the CI unfrozen.