Bump nbsphinx from 0.9.5 to 0.9.6 in /requirements (#1977)

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.9.5 to 0.9.6.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.9.5...0.9.6)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Paul Profizi <[email protected]>

requirements/requirements_docs.txt

@@ -3,7 +3,7 @@ enum-tools[sphinx]==0.12.0
 graphviz==0.20.1
 imageio==2.36.0
 imageio-ffmpeg==0.5.1
-nbsphinx==0.9.5
+nbsphinx==0.9.6
 pypandoc==1.14
 pytest-sphinx==0.6.3
 pyvista==0.44.2