chore(deps): update httpx requirement in /api-server

---
updated-dependencies:
- dependency-name: httpx
  dependency-version: 0.28.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

api-server/requirements.txt

@@ -1,4 +1,4 @@
 fastapi>=0.115.0
 uvicorn[standard]>=0.51.0
-httpx>=0.27.0
+httpx>=0.28.1
 pydantic>=2.13.4