fix: backend/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-REQUESTS-10305723

Author: snyk-bot

backend/requirements.txt

@@ -31,7 +31,7 @@ pydantic==2.0.2
 PyJWT==1.7.1
 python-multipart==0.0.6
 PyYAML==6.0.1
-requests==2.31.0
+requests==2.32.4
 six==1.16.0
 sh==1.14.3
 # SQLAlchemy==2.0.20