fix: test-requirements.txt to reduce vulnerabilities (#50)

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

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

Author: devinlundberg

test-requirements.txt

@@ -7,4 +7,4 @@ fixtures
 mock
 sphinx
 sphinx_rtd_theme
-setuptools>=70.0.0 # not directly required, pinned by Snyk to avoid a vulnerability
+setuptools>=78.1.1 # not directly required, pinned by Snyk to avoid a vulnerability