auto track ldmx-sw releases within CI testing

[tomeichlersmith]

I've done something similar for updating the testing for denv: https://github.com/tomeichlersmith/denv/blob/main/.github/workflows/runner-dependabot.yml

The basic idea is

• keep track of versions to be tested in some file that is not within the .github directory¹
• scheduled workflow that just looks to see if there was a release in the repo we are tracking and makes a PR on the version-tracking file if a new release has been made

I'd like to improve on this design a bit since instead of tracking multiple repos, I'd like to more finely test a single repo. With this in mind, I think an additional feature for the PR-creation is to bump patches while keeping major/minor releases.

Footnotes

1. We have to keep the file outside of the .github directory since GitHub prevents actions from pushing changes to anything in that directory presumably to avoid actions changing their own code in a confusing or malicious way. ↩