piggyback: improve ci setup; account for duplicate runs

Author: m1rm

.github/workflows/ci.yml

@@ -5,6 +5,10 @@ on:
     pull_request:
     workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
     lint:
         runs-on: ubuntu-latest