chore: update fullsend shim workflow

Update the shim workflow to match the current template
in the .fullsend config repo.

Author: fullsend-ai-fullsend[bot]

.github/workflows/fullsend.yaml

@@ -23,7 +23,7 @@ permissions:
   contents: read
   pull-requests: read
 
-"on":
+on:
   issues:
     types: [opened, edited, labeled]
   issue_comment: