feat: On demand staging deployments

Author: nlemoine

.github/workflows/deploy-staging.yml

@@ -66,7 +66,7 @@ jobs:
         uses: wadackel/checkbox-workflow-action@v1
         with:
           id: pr-staging-deploy
-          number: ${{ github.event.issue.number }}
+          number: ${{ github.event.pull_request.number || github.event.issue.number }}
 
       - name: Check deploy checkbox state
         id: deploy-check