ci: prevent deploy workflow from running when CI workflow failed

Author: mschoettle

.github/workflows/cd.yml

@@ -16,6 +16,9 @@ on:
 jobs:
   deployment:
     runs-on: ubuntu-latest
+    # only run if CI workflow completed successfully
+    # https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#running-a-workflow-based-on-the-conclusion-of-another-workflow
+    if: ${{ github.event.workflow_run.conclusion == 'success' }}
     environment: staging
     steps:
       - name: Deploy