Update httpx Dependency to Support Version 0.28.1

Hi Taskbadger team,

I’m currently using pydantic-ai-slim[google], which requires httpx>=0.28.1. However, taskbadger currently pins an older version of httpx, which creates a version conflict.

Would it be possible to update the httpx dependency to allow compatibility with 0.28.1?

Thanks for your work on this project!
