fix: gpt4all-api/gpt4all_api/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-3164749
- https://snyk.io/vuln/SNYK-PYTHON-CERTIFI-5805047
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-5595532
- https://snyk.io/vuln/SNYK-PYTHON-UJSON-2359034
- https://snyk.io/vuln/SNYK-PYTHON-UJSON-2940619
- https://snyk.io/vuln/SNYK-PYTHON-UJSON-2942122

gpt4all-api/gpt4all_api/requirements.txt

@@ -1,12 +1,13 @@
 aiohttp>=3.6.2
 aiofiles
 pydantic>=1.4.0,<2.0.0
-requests>=2.24.0
-ujson>=2.0.2
+requests>=2.31.0
+ujson>=5.4.0
 fastapi>=0.95.0
 Jinja2>=3.0
 gpt4all>=1.0.0
 pytest
 openai
 black
-isort
+isort
+certifi>=2023.7.22 # not directly required, pinned by Snyk to avoid a vulnerability