Make test workflow cancelable

Author: mdpiper

.github/workflows/test.yml

@@ -6,6 +6,10 @@ on:
   schedule:
     - cron: '17 4 3 * *'  # 4:17a on third day of the month
 
+concurrency:
+  group: ${{ github.ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 env:
   BUILD_DIR: _build