Bump markdown from 2.6.6 to 3.8.1 in /modules/sync (#276)

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 2.6.6 to 3.8.1.
- [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/commits/3.8.1)

---
updated-dependencies:
- dependency-name: markdown
  dependency-version: 3.8.1
  dependency-type: direct:production
...

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modules/sync/requirements.txt

@@ -1,6 +1,6 @@
 cssselect==0.9.2
 lxml==4.9.1
-Markdown==2.6.6
+Markdown==3.8.1
 Pillow==12.1.1
 pymongo==4.6.3
 PyPDF2==1.27.9