Update 'Build' badge in README

Author: joshuay03

README.md

@@ -1,7 +1,7 @@
 # AtomicRuby
 
 ![Version](https://img.shields.io/gem/v/atomic-ruby)
-![Build](https://img.shields.io/github/actions/workflow/status/joshuay03/atomic-ruby/.github/workflows/main.yml?branch=main)
+![Build](https://badge.buildkite.com/42198db99cf0eb852d54a6f125d99e68a5c0cd2e1d63026913.svg)
 
 Atomic ([CAS](https://en.wikipedia.org/wiki/Compare-and-swap)) primitives for Ruby.