fix: requirements.txt to reduce vulnerabilities (#62)

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-SETUPTOOLS-3180412

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

Author: camilamaia

requirements.txt

@@ -7,3 +7,4 @@ django-rest-auth==0.9.5
 djangorestframework==3.12.4
 gunicorn==20.0.4
 uritemplate==3.0.1
+setuptools>=65.5.1 # not directly required, pinned by Snyk to avoid a vulnerability