pip prod(deps): update nbsphinx requirement from <=0.9.3 to <=0.9.4

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@0.1.0...0.9.4)

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

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

pyproject.toml

@@ -35,7 +35,7 @@ anndata = { optional = true, version = ">=0.7.6,<0.10.0" }
 black = { optional = true, version = "*" }
 pytest-cov = { optional = true, version = "*" }
 sphinx = { optional = true, version = "<7" }                         # see issue at https://github.com/readthedocs/readthedocs.org/issues/10279
-nbsphinx = { optional = true, version = "<=0.9.3" }
+nbsphinx = { optional = true, version = "<=0.9.4" }
 sphinx-autodoc-typehints = { optional = true, version = "<=1.23.0" }
 sphinx_rtd_theme = { optional = true, version = "<=2.0.0" }
 readthedocs-sphinx-ext = { optional = true, version = "<=2.2.5" }