fix: requirements/dev.txt to reduce vulnerabilities

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

requirements/dev.txt

@@ -15,5 +15,5 @@ notebook>=6.4.12 # not directly required, pinned by Snyk to avoid a vulnerabilit
 prompt-toolkit>=3.0.13 # not directly required, pinned by Snyk to avoid a vulnerability
 pygments>=2.15.0 # not directly required, pinned by Snyk to avoid a vulnerability
 setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability
-tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability
 jupyter-server>=2.11.2 # not directly required, pinned by Snyk to avoid a vulnerability