fix: packages/python/plotly/test_requirements/requirements_39_optional.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-SETUPTOOLS-9964606

Author: snyk-bot

packages/python/plotly/test_requirements/requirements_39_optional.txt

@@ -19,3 +19,4 @@ matplotlib==2.2.3
 scikit-image==0.18.1
 psutil==5.7.0
 kaleido
+setuptools>=78.1.1 # not directly required, pinned by Snyk to avoid a vulnerability