fix: samples/server/petstore/python-fastapi/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-H11-10293728

Author: snyk-bot

samples/server/petstore/python-fastapi/requirements.txt

@@ -11,7 +11,7 @@ fastapi==0.115.2
 graphene==2.1.8
 graphql-core==2.3.2
 graphql-relay==2.0.1
-h11==0.12.0
+h11==0.16.0
 httptools>=0.3.0,<0.7.0
 httpx==0.24.1
 idna==3.7