Bump nbsphinx from 0.8.9 to 0.9.3 in /extra_requirements

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.8.9 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@0.8.9...0.9.3)

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

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

extra_requirements/requirements-docs.txt

@@ -5,7 +5,7 @@ scipy==1.9.1
 commonmark==0.9.1
 gitpython==3.1.35
 graphviz==0.20.1
-nbsphinx==0.8.9
+nbsphinx==0.9.3
 recommonmark==0.7.1
 sphinx==5.2.3
 sphinx_rtd_theme==1.0.0