ci: add concurrency settings for CI workflow

Author: manu4543

.github/workflows/ci.yml

@@ -2,10 +2,16 @@ name: CI
 
 on:  
   push:
+    branches:
+      - master
   pull_request:
     branches:
       - master
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-and-test: