fix: requirements/requirements_docs.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-10390193
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-10390194

Author: snyk-bot

requirements/requirements_docs.txt

@@ -4,3 +4,4 @@ setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerabil
 sphinx
 #m2r2>=0.2.0
 sphinxcontrib-programoutput
+urllib3>=2.5.0 # not directly required, pinned by Snyk to avoid a vulnerability