fix: backend/requirements.txt to reduce vulnerabilities (#33)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-URLLIB3-7267250

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

backend/requirements.txt

@@ -28,7 +28,7 @@ pyjwt==2.4.0
 psutil==5.8.0
 websockets==10.3
 setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability
-urllib3>=1.26.5 # not directly required, pinned by Snyk to avoid a vulnerability
+urllib3>=2.2.2 # not directly required, pinned by Snyk to avoid a vulnerability
 starlette>=0.25.0 # not directly required, pinned by Snyk to avoid a vulnerability
 cryptography>=41.0.5 # not directly required, pinned by Snyk to avoid a vulnerability
 zipp>=3.19.1 # not directly required, pinned by Snyk to avoid a vulnerability