Bump markdown from 3.8.2 to 3.9

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] <support@github.com>

Author: dependabot[bot]

requirements.txt

@@ -3,7 +3,7 @@ asgiref==3.9.1
 httplib2==0.30.0
 backports.zoneinfo;python_version<"3.9"
 feedparser==6.0.11
-Markdown==3.8.2 # pyup: < 3
+Markdown==3.9 # pyup: < 3
 psycopg[binary]==3.2.9
 versiontools==1.9.1
 statsd==4.0.1