Kill previous CI jobs when new pushed

.github/workflows/miri.yml

@@ -38,7 +38,9 @@ env:
   # - tokio-stream/Cargo.toml
   # rust_min: 1.49.0
 
-
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
 
 jobs:
   test: