Bump nbconvert from 7.11.0 to 7.12.0

Bumps [nbconvert](https://github.com/jupyter/nbconvert) from 7.11.0 to 7.12.0.
- [Release notes](https://github.com/jupyter/nbconvert/releases)
- [Changelog](https://github.com/jupyter/nbconvert/blob/main/CHANGELOG.md)
- [Commits](jupyter/nbconvert@v7.11.0...v7.12.0)

---
updated-dependencies:
- dependency-name: nbconvert
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]