fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7642790
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7642791
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7642813
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-7642814

requirements.txt

@@ -1,4 +1,4 @@
-django>=3.1.1,<4.0
+django>=4.2.15
 djangosaml2>=1.0.0
 pysaml2>=6.5.1
 cffi