add _target for forked repo support

.github/workflows/pr-labels.yaml

@@ -1,7 +1,7 @@
 name: Manage labels based on PR body
 
 on:
-  pull_request:
+  pull_request_target:
     types: [opened, edited, reopened, synchronize]
 
 jobs:
@@ -53,4 +53,4 @@ jobs:
               -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" \
               -H "Accept: application/vnd.github.v3+json" \
               https://api.github.com/repos/${{ github.repository }}/issues/${{ github.event.pull_request.number }}/labels/$label
-          done
+          done