cancel previous runs (karafka#312)

Author: mensfeld

.github/workflows/ci.yml

@@ -1,6 +1,8 @@
 name: ci
 
-concurrency: ci-${{ github.ref }}
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 
 on:
   pull_request: