Update build.yml

.github/workflows/build.yml

@@ -4,6 +4,14 @@ on:
   pull_request:
     branches: [ '**' ]
   merge_group:
+  
+# When pushing a new commit we should
+# cancel the previous test run to not
+# consume more runners than we need to.
+concurrency:
+  group: ${{ github.head_ref }}
+  cancel-in-progress: true
+
 
 jobs:
   build-core: