Bump markdown from 3.5.1 to 3.5.2 in /docs

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.5.1 to 3.5.2.
- [Release notes](https://github.com/Python-Markdown/markdown/releases)
- [Changelog](https://github.com/Python-Markdown/markdown/blob/master/docs/changelog.md)
- [Commits](Python-Markdown/markdown@3.5.1...3.5.2)

---
updated-dependencies:
- dependency-name: markdown
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

docs/requirements.txt

@@ -5,7 +5,7 @@ colorama==0.4.6
 ghp-import==2.1.0
 idna==3.6
 Jinja2==3.1.3
-Markdown==3.5.1
+Markdown==3.5.2
 MarkupSafe==2.1.3
 mdx-truly-sane-lists==1.3
 mergedeep==1.3.4