chore(deps): update dependency nbsphinx to v0.9.4 (#673)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [nbsphinx](https://nbsphinx.readthedocs.io/) | `==0.9.3` -> `==0.9.4`
|
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docs/requirements.txt

@@ -1,7 +1,7 @@
 myst-parser==2.0.0
 rstcheck==6.2.1
 sphinx==7.3.7
-nbsphinx==0.9.3
+nbsphinx==0.9.4
 sphinx-autobuild==2024.4.16
 sphinx-markdown-parser==0.2.4
 sphinxcontrib-actdiag==3.0.0