Revert "Remove branch from preview_deploy.yml (#5523)"

This reverts commit e2075bd.

Author: joshblack

.github/workflows/deploy_preview.yml

@@ -1,6 +1,8 @@
 name: Deploy Preview
 on:
   workflow_run:
+    branches:
+      - main
     workflows: [CI]
     types:
       - completed