feat: trigger preview workflow on pull request closure (#3956)

.github/workflows/fly-pr-preview.yml

@@ -3,7 +3,7 @@ on:
   # Run this workflow on every PR event. Existing review apps will be updated when the PR is updated.
   pull_request_target:
     # Trigger when labels are changed or more commits added to a PR that contains labels
-    types: [labeled, synchronize]
+    types: [closed, labeled, synchronize]
     # Only create a preview if changes have been made to the main src code or backend functions
     paths:
       - 'src/**'