cancel concurrent CI runs

Author: rmalmain

.github/workflows/main.yml

@@ -2,6 +2,11 @@ on:
   workflow_dispatch:
   push:
   pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-and-test:
     runs-on: ubuntu-latest