ci: cancel current runs on new trigger

.github/workflows/main.yml

@@ -10,6 +10,10 @@ on:
     branches: 
       - master
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 jobs:
   tests:
     name: Run tests