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

@@ -1,3 +1,4 @@
 selenium>=4.9.0
 percy-selenium>=2.1.2
 requests>=2.31.0
+urllib3>=2.6.3 # not directly required, pinned by Snyk to avoid a vulnerability