Bump markdown from 3.3.7 to 3.4.3

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.3.7 to 3.4.3.
- [Release notes](https://github.com/Python-Markdown/markdown/releases)
- [Changelog](https://github.com/Python-Markdown/markdown/blob/master/docs/change_log/release-2.6.md)
- [Commits](https://github.com/Python-Markdown/markdown/compare/3.3.7...3.4.3)

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

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

docs/requirements-docs.txt

@@ -1,4 +1,4 @@
-markdown==3.3.7
+markdown==3.4.3
 mkdocs==1.4.2
 mkdocs-material==9.1.5
 mdx_truly_sane_lists==1.3