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

@@ -8,3 +8,4 @@ chardet==3.0.4
 Django~=3.2.22
 aiohttp>=3.9.0 # not directly required, pinned by Snyk to avoid a vulnerability
 sqlparse>=0.5.0 # not directly required, pinned by Snyk to avoid a vulnerability
+urllib3>=2.6.3 # not directly required, pinned by Snyk to avoid a vulnerability