Bump mistune from 2.0.3 to 3.2.1 in /docs (#132)

Bumps [mistune](https://github.com/lepture/mistune) from 2.0.3 to 3.2.1.
- [Release notes](https://github.com/lepture/mistune/releases)
- [Changelog](https://github.com/lepture/mistune/blob/main/docs/changes.rst)
- [Commits](lepture/mistune@v2.0.3...v3.2.1)

---
updated-dependencies:
- dependency-name: mistune
  dependency-version: 3.2.1
  dependency-type: direct:production
...

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Author: dependabot[bot]

docs/requirements.txt

@@ -24,7 +24,7 @@ jupyter-core==4.11.2
 jupyterlab-pygments==0.1.2
 lxml==6.1.0
 MarkupSafe==1.1.1
-mistune==2.0.3
+mistune==3.2.1
 nbclient==0.5.1
 nbconvert==7.17.1
 nbformat==5.0.8