add passing/failing badge for default branch

Author: Carsons-Eels

README.md

@@ -2,6 +2,7 @@
 
 [![GitPOAP Badge](https://public-api.gitpoap.io/v1/repo/ethereum/execution-specs/badge)](https://www.gitpoap.io/gh/ethereum/execution-specs)
 [![codecov](https://codecov.io/gh/ethereum/execution-specs/graph/badge.svg?token=0LQZO56RTM)](https://codecov.io/gh/ethereum/execution-specs)
+[![Python Specification](https://github.com/ethereum/execution-specs/actions/workflows/test.yaml/badge.svg)](https://github.com/ethereum/execution-specs/actions/workflows/test.yaml)
 
 ## Description