Update httpx requirement from ^0.23 to >=0.23,<0.28 (#238)

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@0.23.0...0.27.2)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pyproject.toml

@@ -20,7 +20,7 @@ python = "^3.8"
 typing-extensions = {version = "^4.0.0", python = "<3.10"}
 requests = {version = "*", optional = true}
 pydantic = {version = ">=2.0,<3.0", optional = true}
-httpx = {version = "^0.23", optional = true}
+httpx = {version = ">=0.23,<0.28", optional = true}
 
 [tool.poetry.dev-dependencies]
 pytest = "*"