fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-14896210

Author: snyk-bot

requirements.txt

@@ -5,3 +5,4 @@ apppath
 sorcery
 sphinxcontrib-programoutput
 #mistune==0.8.4 #mistune>=2.0.1 # not directly required, pinned by Snyk to avoid a vulnerability
+urllib3>=2.6.3 # not directly required, pinned by Snyk to avoid a vulnerability