Always commit citation cache

[vincerubinetti]

The citation process automatically caches network requests (immediately, at a per-request level) and stores them in _cite/.cache/cache.db. However, when running the citation process on GitHub Actions, changes to this .db file go away after each run unless explicitly kept. If you look at update-citations.yaml, the "commit updated citations" step happens after running the main cite.py script. If the cite script fails for any reason (e.g. some sources couldn't be cited), it will skip all the remaining steps of the job, and the work that was actually successful and cached in that workflow run will be lost. As such, we should add a "Commit cache" step immediately after the cite script step, which uses stefanzweifel/git-auto-commit-action@v5 but only commits cache.db, and always runs even if the cite script step fails. Make use of always() and/or continue-on-error.