Add concurrency control to cancel in-progress PR workflows

Author: TTOzzi

.github/workflows/pull_request.yml

@@ -3,6 +3,10 @@ name: Pull request
 on:
   pull_request:
     types: [opened, reopened, synchronize]
+    
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 jobs:
   tests: