Fix build badge since switching to github actions

README.md

@@ -1,7 +1,7 @@
 Minetest
 ========
 
-![Build Status](https://github.com/minetest/minetest/workflows/validate/badge.svg)
+![Build Status](https://github.com/minetest/minetest/workflows/build/badge.svg)
 [![Translation status](https://hosted.weblate.org/widgets/minetest/-/svg-badge.svg)](https://hosted.weblate.org/engage/minetest/?utm_source=widget)
 [![License](https://img.shields.io/badge/license-LGPLv2.1%2B-blue.svg)](https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html)