fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-10302884
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-10305723

Author: snyk-bot

requirements.txt

@@ -1,7 +1,8 @@
-Django>=4.0,<6
+Django>=4.2.22
 Sphinx>=1.2.0
 phonenumbers>=7.0.2
 django-phonenumber-field==6.1.0
 twilio>=7
 wheel>=0.22.0
 setuptools>=36.2
+requests>=2.32.4 # not directly required, pinned by Snyk to avoid a vulnerability