add branch query on test badge in README.md (#1112)

Author: ischneider

README.md

@@ -1,6 +1,6 @@
 # Planet SDK for Python
 
-[![Build Status](https://github.com/planetlabs/planet-client-python/actions/workflows/test.yml/badge.svg)](https://github.com/planetlabs/planet-client-python/actions/workflows/test.yml)
+[![Build Status](https://github.com/planetlabs/planet-client-python/actions/workflows/test.yml/badge.svg?branch=main)](https://github.com/planetlabs/planet-client-python/actions/workflows/test.yml)
 [![PyPI Downloads](https://static.pepy.tech/badge/planet)](https://pepy.tech/projects/planet)
 
 The [Planet](https://planet.com) Software Development Kit (SDK) for Python