Bump markdown from 3.6 to 3.7

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.6 to 3.7.
- [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@3.6...3.7)

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

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

requirements/base.txt

@@ -16,7 +16,7 @@ django-simple-history==3.7.0
 django-tree-queries==0.19.0
 django-uuslug==2.0.0
 jira==3.8.0
-Markdown==3.6
+Markdown==3.7
 PyGithub==2.3.0
 Pygments==2.18.0
 python-gitlab==4.9.0