Update httpx requirement from >=0.27.0 to >=0.28.1

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@0.27.0...0.28.1)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -39,7 +39,7 @@ dev = [
     "pytest>=8.0.0",
     "pytest-cov>=4.1.0",
     "pytest-asyncio>=0.23.0",
-    "httpx>=0.27.0",
+    "httpx>=0.28.1",
     "ruff>=0.3.0",
     "mypy>=1.8.0",
 ]