Bump nbsphinx from 0.8.12 to 0.9.3

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.8.12 to 0.9.3.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.8.12...0.9.3)

---
updated-dependencies:
- dependency-name: nbsphinx
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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