fix: requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-1066259
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-1279042
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-1290072
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-1298665
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-2312875
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-2329158
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-2329159
- https://snyk.io/vuln/SNYK-PYTHON-DJANGO-2329160
- https://snyk.io/vuln/SNYK-PYTHON-DJANGORESTFRAMEWORK-1090569