ci: cancel in-progress h2-compliance runs on new commits

Author: codeadict

.github/workflows/h2-compliance.yml

@@ -8,6 +8,10 @@ on:
   # Allow manual trigger
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   h2spec_compliance:
     name: HTTP/2 Compliance (h2-client-test-harness)