cancel previous tests

Author: hiroshihorie

.github/workflows/testing-matrix.yaml

@@ -5,6 +5,10 @@ on:
   push:
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   run_all_tests:
     strategy: