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>=3.2.19,<5
+Django>=4.2.15
 
 git+https://github.com/UniversitaDellaCalabria/django-admin-search-builder.git
 django_ckeditor>=5.9.0