Update danger to run on pull_request_target

pull_request_target runs in the context of the base repo, which should allow Danger to be able to comment on things from outside the repo: https://docs.github.com/en/actions/reference/events-that-trigger-workflows#pull_request_target

.github/workflows/danger.yml

@@ -1,7 +1,7 @@
 name: Danger
 on:
   workflow_dispatch:
-  pull_request:
+  pull_request_target:
     types: [synchronize, edited, opened, reopened]
 jobs:
   run: