fix: use event payload ref and guard auto-merge on closed events for auto merge workflow

Author: jlin27

.github/workflows/auto-merge-openapi-updates.yml

@@ -2,12 +2,12 @@ name: Auto-merge OpenAPI updates
 on:
   pull_request:
     types: [opened, synchronize, closed]
-
 jobs:
   auto-merge:
     if: |
+      github.event.action != 'closed' &&
       github.event_name == 'pull_request' &&
-      startsWith(github.head_ref, 'auto/update-openapi') &&
+      startsWith(github.event.pull_request.head.ref, 'auto/update-openapi') &&
       github.event.pull_request.head.repo.full_name == github.repository &&
       github.event.pull_request.user.login == '0x-automation[bot]'
     runs-on: ubuntu-latest
@@ -23,12 +23,11 @@ jobs:
       - name: Log merge status
         run: |
           echo "✅ Auto-merge enabled for PR: ${{ github.event.pull_request.html_url }}"
-
   publish-after-merge:
     if: |
       github.event_name == 'pull_request' &&
       github.event.pull_request.merged == true &&
-      startsWith(github.head_ref, 'auto/update-openapi') &&
+      startsWith(github.event.pull_request.head.ref, 'auto/update-openapi') &&
       github.event.pull_request.user.login == '0x-automation[bot]'
     runs-on: ubuntu-latest
     permissions: