fix: backend/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-FASTAPI-6228055

backend/requirements.txt

@@ -13,7 +13,7 @@ click==8.0.3
 colorama==0.4.4
 coverage==6.0.2
 distlib==0.3.3
-fastapi==0.70.0
+fastapi==0.109.1
 fastapi-pagination==0.9.1
 filelock==3.3.1
 h11==0.12.0