fix: update GitHub workflow badge URL and fix PyYAML compatibility

- Update GitHub workflow badge to use new format (CI.yml instead of workflow name)
- Update PyYAML from 5.4.1 to 6.0.3 for Python 3.12 compatibility
- Fixes CD workflow failure: AttributeError: cython_sources

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Author: semarj

README.md

@@ -3,7 +3,7 @@
 ShipEngine Python SDK
 =====================
 
-![GitHub Workflow Status](https://img.shields.io/github/workflow/status/ShipEngine/shipengine-python/Python%20package?label=shipengine-python&logo=github&logoColor=white)
+![GitHub Workflow Status](https://img.shields.io/github/actions/workflow/status/ShipEngine/shipengine-python/CI.yml?branch=main&label=shipengine-python&logo=github&logoColor=white)
 [![Coverage Status](https://coveralls.io/repos/github/ShipEngine/shipengine-python/badge.svg?branch=main)](https://coveralls.io/github/ShipEngine/shipengine-python?branch=main)
 ![GitHub](https://img.shields.io/github/license/shipengine/shipengine-python?color=blue)
 ![OS Compatibility](https://shipengine.github.io/img/badges/os-badges.svg)