Add workflow concurrency settings

Author: jtraglia

.github/workflows/check-specrefs.yml

@@ -1,4 +1,9 @@
 name: Check Spec References
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: [unstable, stable]