chore(deps): bump markdown from 3.6 to 3.7 in /backend

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](https://github.com/Python-Markdown/markdown/compare/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>

backend/requirements.txt

@@ -45,7 +45,7 @@ pypdf==4.3.1
 docx2txt==0.8
 python-pptx==1.0.0
 unstructured==0.15.7
-Markdown==3.6
+Markdown==3.7
 pypandoc==1.13
 pandas==2.2.2
 openpyxl==3.1.5