build(deps): bump markdown from 3.7 to 3.8

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.7 to 3.8.
- [Release notes](https://github.com/Python-Markdown/markdown/releases)
- [Changelog](https://github.com/Python-Markdown/markdown/blob/master/docs/changelog.md)
- [Commits](https://github.com/Python-Markdown/markdown/compare/3.7...3.8)

---
updated-dependencies:
- dependency-name: markdown
  dependency-version: '3.8'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements-docs.txt

@@ -86,7 +86,7 @@ jinja2==3.1.6
     #   mkdocstrings
 jsmin==3.0.1
     # via mkdocs-minify-plugin
-markdown==3.7
+markdown==3.8
     # via
     #   mkdocs
     #   mkdocs-autorefs