build(deps-dev): update httpx requirement

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@0.24.1...0.28.0)

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

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

Author: dependabot[bot]

pyproject.toml

@@ -21,7 +21,7 @@ pytest = ">=7.1.2,<9.0.0"
 pytest-cov = ">=3,<6"
 pytest-asyncio = ">=0.21.1,<0.25.0"
 tox = ">=3.26,<5.0"
-httpx = ">=0.24.1,<0.28.0"
+httpx = ">=0.24.1,<0.29.0"
 ruff = ">=0.5.0,<0.9.0"
 pyright = ">=1.1.350,<1.2"