fix: doc/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-JUPYTERSERVER-17152947
- https://snyk.io/vuln/SNYK-PYTHON-JUPYTERSERVER-17391532
- https://snyk.io/vuln/SNYK-PYTHON-TORNADO-17356157

Author: snyk-bot

doc/requirements.txt

@@ -20,3 +20,5 @@ notebook
 sphinx-autodoc-typehints
 fonttools>=4.43.0 # not directly required, pinned by Snyk to avoid a vulnerability
 jupyterlab>=4.4.8 # not directly required, pinned by Snyk to avoid a vulnerability
+jupyter-server>=2.20.0 # not directly required, pinned by Snyk to avoid a vulnerability
+tornado>=6.5.7 # not directly required, pinned by Snyk to avoid a vulnerability