Cancel in-progress slow tests on push

.github/workflows/cislowtestmode.yml

@@ -3,11 +3,15 @@ name: CI Slow
 
 on:
     push:
-        branches:
-            - main
-            - develop
+        branches-ignore:
+            - classic*
     workflow_dispatch:
-    pull_request:
+
+concurrency:
+  # Use github.run_id on main or develop branch (unlimited concurrency)
+  # Use github.ref otherwise, so that it's unique per branch or PR
+  group: ${{ github.workflow }}-${{ github.ref_protected && github.run_id || github.ref }}
+  cancel-in-progress: true
 
 jobs:
     citestmode: