fix: docs/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-8400708

docs/requirements.txt

@@ -5,7 +5,7 @@ sphinx-copybutton
 sphinx-autobuild
 sphinxext-opengraph
 numpy>=1.22.2 # not directly required, pinned by Snyk to avoid a vulnerability
-tornado>=6.4.1 # not directly required, pinned by Snyk to avoid a vulnerability
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability
 pillow>=10.3.0 # not directly required, pinned by Snyk to avoid a vulnerability
 fonttools>=4.43.0 # not directly required, pinned by Snyk to avoid a vulnerability
 zipp>=3.19.1 # not directly required, pinned by Snyk to avoid a vulnerability