Update mistune requirement from <3 to <4 (#399)

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@v0.1.0...v3.0.1)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pyproject.toml

@@ -61,7 +61,7 @@ docs = [
   "sphinx-copybutton",
   "sphinxcontrib-openapi>0.8",
   "myst-parser",
-  "mistune<3",
+  "mistune<4",
   "jinja2<3.2.0"
 ]
 openapi = [