Update httpx requirement from ~=0.27.2 to ~=0.28.1 in /code/function

Updates the requirements on [httpx](https://github.com/encode/httpx) to permit the latest version.
- [Release notes](https://github.com/encode/httpx/releases)
- [Changelog](https://github.com/encode/httpx/blob/master/CHANGELOG.md)
- [Commits](encode/httpx@0.27.2...0.28.1)

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

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

Author: dependabot[bot]

code/function/requirements.txt

@@ -6,7 +6,7 @@
 azure-functions~=1.21.3
 fastapi~=0.115.6
 pydantic-settings~=2.7.0
-httpx~=0.27.2
+httpx~=0.28.1
 azure-monitor-opentelemetry-exporter==1.0.0b32
 opentelemetry-instrumentation-fastapi==0.49b2
 opentelemetry-instrumentation-httpx~=0.49b2