Bump markdown from 3.8.2 to 3.9 in /requirements

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.8.2 to 3.9.
- [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@3.8.2...3.9.0)

---
updated-dependencies:
- dependency-name: markdown
  dependency-version: '3.9'
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/common.txt

@@ -12,7 +12,7 @@ docutils==0.21.2
 feedparser==6.0.11
 Jinja2==3.1.6
 libsass==0.23.0
-Markdown==3.8.2
+Markdown==3.9
 Pillow==11.3.0
 psycopg[c]==3.2.9
 Pygments==2.19.2