- I was going through the `sorbet/files.yaml` moving various things to
  `true`, playing around locally, and happened upon some files that it
  was tracking that had been deleted.
- We want to do some automation of new files, but I'm not sure we'd ever
  considered the possibility of code being removed. :-D
- This adds a `--prune-files-list` switch and updates the Tapioca GitHub
  Actions workflow to use it. Any changes to the `sorbet/files.yaml`
  file will be committed as part of the scheduled Tapioca update job.