Update dependency djangorestframework to v3.15.2 [SECURITY]

requirements.txt

@@ -9,7 +9,7 @@ Django==2.2.28
 django-after-response==0.2.2
 django-bootstrap4==22.1
 django-health-check==3.18.3
-djangorestframework==3.13.1
+djangorestframework==3.15.2
 emoji-data-python==1.5.0
 gunicorn==22.0.0
 git+https://github.com/hmcts/[email protected]#egg=response