build(deps): bump nbsphinx from 0.9.7 to 0.9.8 in /docs

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.9.7 to 0.9.8.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.9.7...0.9.8)

---
updated-dependencies:
- dependency-name: nbsphinx
  dependency-version: 0.9.8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -1,7 +1,7 @@
 appdirs==1.4.4
 ipython>=7.0.0
 myst_parser==4.0.1
-nbsphinx==0.9.7
+nbsphinx==0.9.8
 numpy>=1.20.0
 scipy>=1.7.0
 sphinx>=5.2.0