tests: cancel in progress builds when a new commit is pushed

.github/workflows/ci.yml

@@ -10,6 +10,10 @@ on:
     branches:
       - 'master'
 
+concurrency:
+  group: build-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build:
     name: build