Build: Bump prek from 0.2.15 to 0.2.20

Bumps [prek](https://github.com/j178/prek) from 0.2.15 to 0.2.20.
- [Release notes](https://github.com/j178/prek/releases)
- [Changelog](https://github.com/j178/prek/blob/master/CHANGELOG.md)
- [Commits](j178/prek@v0.2.15...v0.2.20)

---
updated-dependencies:
- dependency-name: prek
  dependency-version: 0.2.20
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]