feat: use `renovate` to bump `pre-commit` hook versions

[gforsyth]

Renovate now has a beta for bumping pre-commit hook versions (https://docs.renovatebot.com/modules/manager/pre-commit/) -- I think we should try this out.

kvikio was using a mypy pre-commit hook that was quite old (v1.3.0 vs. v1.20.2) which is part of what is prompting this.

We can enable the beta functionality by adding this to renovate.json:

{
  "pre-commit": {
    "enabled": true
  }
}