Try to support diff url from pull request

action.yml

@@ -20,6 +20,10 @@ inputs:
     description: "An array of commit objects describing the pushed commits"
     required: true
     default: "${{ toJSON(github.event.commits) }}"
+  DIFF_URL:
+    description: "The URL to use to get the diff (automatically set)"
+    required: true
+    default: "${{ github.event.pull_request?.diff_url }}"
   SHA:
     description: "The SHA of the latest commit (automatically set)"
     required: true