On CI, thepre-commit job has two shortcomings:

• It runs on a machine far more powerful than necessary, since anything slow should not be done inpre-commit at all (since some developers may runpre-commit locally).
• We've haven't been using any automated means of keeping the pre-commit hook versions up to date, and as a results some of them are quite old. This includesruff. (There is an external integration that can keep pre-commit hooks up to date on GitHub, but it requires providing access to the repository to an external service. This is sometimes a tradeoff worth making, but it's one we've avoided doing here for this purpose, I think rightly.)

These have both become easier to address recently:

• A lighter-weightubuntu-slim runner is available. Running it on that should work as well and be as fast, and give an indication that we're doing too much inpre-commit if that is ever not the case. It also frees up anubuntu-latest runner, potentially making CI finish slightly earlier in some PRs where there have been a lot of pushes.
• Dependabot now supportspre-commit as a beta ecosystem, so it can keep them up to date. I've tested this in my fork; the resulting grouped PR looks likeEliahKagan#5. It's not ideal that the ecosystem is still in beta, but I think it's worth using--and if it turns out to have bugs I haven't yet observed, then this is an oppportunity for me to report them.

This PR uses theubuntu-slim runner to runpre-commit on CI, and enables Dependabot version updates forpre-commit hooks.