fix: docs/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-SETUPTOOLS-7448482

docs/requirements.txt

@@ -1,4 +1,4 @@
 sphinx>=2.0
 sphinx_rtd_theme
 sphinxcontrib-images
-setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability
+setuptools>=70.0.0 # not directly required, pinned by Snyk to avoid a vulnerability