fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-14192442
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-14192443

Author: snyk-bot

requirements.txt

@@ -2,3 +2,4 @@ lxml
 python-dateutil
 pyyaml
 requests
+urllib3>=2.6.0 # not directly required, pinned by Snyk to avoid a vulnerability