Add concurrency controls to workflow

Author: sd109

.github/workflows/test-pr.yml

@@ -6,6 +6,9 @@ on:
       - reopened
       - ready_for_review
       - synchronize
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref }}
+  cancel-in-progress: true
 jobs:
   chart_validation:
     runs-on: ubuntu-latest