chore: bump markdown from 3.7 to 3.8.1 in /docs (#2405)

Bumps [markdown](https://github.com/Python-Markdown/markdown) from 3.7 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](Python-Markdown/markdown@3.7...3.8.1)

---
updated-dependencies:
- dependency-name: markdown
  dependency-version: 3.8.1
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -39,9 +39,9 @@ jinja2==3.1.6 \
     #   mkdocs
     #   mkdocs-git-revision-date-plugin
     #   mkdocs-macros-plugin
-markdown==3.7 \
-    --hash=sha256:2ae2471477cfd02dbbf038d5d9bc226d40def84b4fe2986e49b59b6b472bbed2 \
-    --hash=sha256:7eb6df5690b81a1d7942992c97fad2938e956e79df20cbc6186e9c3a77b1c803
+markdown==3.8.1 \
+    --hash=sha256:46cc0c0f1e5211ab2e9d453582f0b28a1bfaf058a9f7d5c50386b99b588d8811 \
+    --hash=sha256:a2e2f01cead4828ee74ecca9623045f62216aef2212a7685d6eb9163f590b8c1
     # via mkdocs
 markdown-it-py==3.0.0 \
     --hash=sha256:355216845c60bd96232cd8d8c40e8f9765cc86f46880e43a8fd22dc1a1a8cab1 \