Update httpx requirement from <0.28.0,>=0.21.3 to >=0.21.3,<0.29.0

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@0.21.3...0.28.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

pyproject.toml

@@ -97,7 +97,7 @@ classifiers = [
 dynamic = ["version"]
 requires-python = ">=3.9"
 dependencies = [
-    "httpx >=0.21.3,<0.28.0",
+    "httpx >=0.21.3,<0.29.0",
     "jwcrypto >=1.4,<2.0.0",
 ]