build(deps): update nbsphinx requirement from ~=0.8 to ~=0.9

Updates the requirements on [nbsphinx](https://github.com/spatialaudio/nbsphinx) to permit the latest version.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.8.0...0.9.0)

---
updated-dependencies:
- dependency-name: nbsphinx
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements-docs.txt

@@ -3,7 +3,7 @@ ipython~=8.11
 Sphinx~=5.3
 sphinxcontrib-fulltoc~=1.2
 myst-parser~=1.0.0
-nbsphinx~=0.8
+nbsphinx~=0.9
 jinja2<4.0
 geopandas~=0.12.2
 hvplot~=0.8.2