Bump markdown from 2.6.11 to 3.5

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 2.6.11 to 3.5.
- [Changelog](https://github.com/Python-Markdown/markdown/blob/master/docs/changelog.md)
- [Commits](Python-Markdown/markdown@2.6.11...3.5)

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

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

requirements.txt

@@ -8,7 +8,7 @@ Flask-WTF==1.0.1
 ItsDangerous==2.1.2
 Jinja2==3.1.2
 jira==2.0.0
-Markdown==2.6.11
+Markdown==3.5
 marshmallow==3.20.1
 MarkupSafe==2.1.2
 py-gfm==0.1.4