Update Deno Deploy workflow trigger and concurrency

Change the workflow trigger from push on 'functions' branch to workflow_run on 'main' after 'Sync to Pages and Functions' completes. Add concurrency group to prevent overlapping runs.

.github/workflows/functions-dn.yml

@@ -1,11 +1,18 @@
 name: Deploy to Deno Deploy
 
 on:
-  push:
+  workflow_run:
+    workflows: ["Sync to Pages and Functions"]
+    types:
+      - completed
     branches:
-      - functions
+      - main
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: false
+
 permissions:
   id-token: write
   contents: read