fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7886958
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7886959

requirements.txt

@@ -6,3 +6,4 @@ cryptography>=41.0.4 # not directly required, pinned by Snyk to avoid a vulnerab
 pyjwt>=2.4.0 # not directly required, pinned by Snyk to avoid a vulnerability
 requests>=2.32.0 # not directly required, pinned by Snyk to avoid a vulnerability
 sqlparse>=0.5.0 # not directly required, pinned by Snyk to avoid a vulnerability
+django>=4.2.16 # not directly required, pinned by Snyk to avoid a vulnerability