Fix build status badge

Badges API has changed and our build badge is broken at the moment. This should fix it. See badges/shields#8671 for more context.

README.md

@@ -3,7 +3,7 @@
 
 _Ruler is a Gradle plugin which helps you analyze the size of your Android apps._
 
-[![Build Status](https://img.shields.io/github/workflow/status/spotify/ruler/CI)](https://github.com/spotify/ruler/actions)
+[![Build Status](https://img.shields.io/github/actions/workflow/status/spotify/ruler/ci.yaml?branch=main)](https://github.com/spotify/ruler/actions)
 [![Maven Release](https://img.shields.io/maven-central/v/com.spotify.ruler/ruler-gradle-plugin)](https://github.com/spotify/ruler/releases)
 [![License](https://img.shields.io/github/license/spotify/ruler)](https://github.com/spotify/ruler/blob/main/LICENSE)