Bump nbsphinx from 0.8.12 to 0.9.5

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.8.12 to 0.9.5.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.8.12...0.9.5)

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

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

devtools/dev-requirements.txt

@@ -2,7 +2,7 @@
 -r ../requirements.txt
 
 # building the docs
-nbsphinx == 0.8.12
+nbsphinx == 0.9.5
 sphinx > 3.0.0
 # TODO (#1396): Remove sphinx-argparse <0.5.0 pin once upstream build issue is fixed
 # <https://github.com/sphinx-doc/sphinx-argparse/issues/56>