Bump markdown-it-py from 3.0.0 to 4.0.0 in /docs

Bumps [markdown-it-py](https://github.com/executablebooks/markdown-it-py) from 3.0.0 to 4.0.0.
- [Release notes](https://github.com/executablebooks/markdown-it-py/releases)
- [Changelog](https://github.com/executablebooks/markdown-it-py/blob/master/CHANGELOG.md)
- [Commits](executablebooks/markdown-it-py@v3.0.0...v4.0.0)

---
updated-dependencies:
- dependency-name: markdown-it-py
  dependency-version: 4.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

docs/build_requirements.txt

@@ -34,9 +34,9 @@ imagesize==1.4.1 \
 jinja2==3.1.6 \
   --hash=sha256:0137fb05990d35f1275a587e9aee6d56da821fc83491a0fb838183be43f66d6d \
   --hash=sha256:85ece4451f492d0c13c5dd7c13a64681a86afae63a5f347908daf103ce6d2f67
-markdown_it_py==3.0.0 \
-  --hash=sha256:e3f60a94fa066dc52ec76661e37c851cb232d92f9886b15cb560aaada2df8feb \
-  --hash=sha256:355216845c60bd96232cd8d8c40e8f9765cc86f46880e43a8fd22dc1a1a8cab1
+markdown_it_py==4.0.0 \
+  --hash=sha256:87327c59b172c5011896038353a81343b6754500a08cd7a4973bb48c6d578147 \
+  --hash=sha256:cb0a2b4aa34f932c007117b194e945bd74e0ec24133ceb5bac59009cda1cb9f3
 mdit_py_plugins==0.5.0 \
   --hash=sha256:07a08422fc1936a5d26d146759e9155ea466e842f5ab2f7d2266dd084c8dab1f \
   --hash=sha256:f4918cb50119f50446560513a8e311d574ff6aaed72606ddae6d35716fe809c6