Fix check-merge workflow on PRs from forks (#10366)

.github/workflows/check-merge.yml

@@ -1,6 +1,6 @@
 name: Check mergeability
 
-on: pull_request
+on: pull_request_target
 
 permissions:
   pull-requests: write
@@ -35,6 +35,7 @@ jobs:
       - uses: actions/checkout@v4
         if: steps.blocked.outputs.result != 'true'
         with:
+          repository: ${{ github.event.pull_request.head.repo.full_name }}
           fetch-depth: 0
 
       - name: Get changed files in the .changeset folder