fix: example/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-CRYPTOGRAPHY-15809188

Author: snyk-bot

example/requirements.txt

@@ -6,3 +6,4 @@ setuptools>=70.0.0 # not directly required, pinned by Snyk to avoid a vulnerabil
 werkzeug>=3.0.1 # not directly required, pinned by Snyk to avoid a vulnerability
 requests>=2.32.2 # not directly required, pinned by Snyk to avoid a vulnerability
 urllib3>=2.2.2 # not directly required, pinned by Snyk to avoid a vulnerability
+cryptography>=46.0.6 # not directly required, pinned by Snyk to avoid a vulnerability