Fix GitHub Actions badge in README (pydata#10155)

Author: spencerkclark

README.md

@@ -1,6 +1,6 @@
 # xarray: N-D labeled arrays and datasets
 
-[![CI](https://github.com/pydata/xarray/workflows/CI/badge.svg?branch=main)](https://github.com/pydata/xarray/actions?query=workflow%3ACI)
+[![CI](https://github.com/pydata/xarray/actions/workflows/ci.yaml/badge.svg?branch=main)](https://github.com/pydata/xarray/actions/workflows/ci.yaml?query=branch%3Amain)
 [![Code coverage](https://codecov.io/gh/pydata/xarray/branch/main/graph/badge.svg?flag=unittests)](https://codecov.io/gh/pydata/xarray)
 [![Docs](https://readthedocs.org/projects/xray/badge/?version=latest)](https://docs.xarray.dev/)
 [![Benchmarked with asv](https://img.shields.io/badge/benchmarked%20by-asv-green.svg?style=flat)](https://asv-runner.github.io/asv-collection/xarray/)