Update mistune requirement from 0.8.4 to 3.1.1

Updates the requirements on [mistune](https://github.com/lepture/mistune) to permit the latest version.
- [Release notes](https://github.com/lepture/mistune/releases)
- [Changelog](https://github.com/lepture/mistune/blob/master/docs/changes.rst)
- [Commits](lepture/mistune@v0.8.4...v3.1.1)

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

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

pyproject.toml

@@ -49,7 +49,7 @@ nbsphinx = { version = "*", optional = true }
 recommonmark = { version = "*", optional = true }
 graphviz = { version = "*", optional = true }
 m2r = { version = "*", optional = true }
-mistune = { version = "0.8.4", optional = true }
+mistune = { version = "3.1.1", optional = true }
 urllib3 = { version = "2.2.2", optional = true }
 lxml_html_clean = { version = "*", optional = true }