[+] Update preview.yml

This reverts commit b66f206284.

.github/workflows/preview.yml

@@ -9,9 +9,6 @@ on:
       pr_number:
         description: 'Pull Request number to deploy preview for'
         required: true
-      pr_branch:
-        description: 'The branch name to deploy'
-        required: true
 
 jobs:
   build:
@@ -33,17 +30,15 @@ jobs:
         run: |
           if [ "${{ github.event_name }}" == "workflow_dispatch" ]; then
             echo "PR_NUMBER=${{ github.event.inputs.pr_number }}" >> $GITHUB_ENV
-            echo "PR_BRANCH=${{ github.event.inputs.pr_branch }}" >> $GITHUB_ENV
           else
             echo "PR_NUMBER=${{ github.event.pull_request.number }}" >> $GITHUB_ENV
-            echo "PR_BRANCH=${{ github.event.pull_request.head.ref }}" >> $GITHUB_ENV
           fi
 
       # Now check out the PR’s head branch (whether from a PR event or supplied manually)
       - name: Checkout PR branch
         uses: actions/checkout@v4
         with:
-          ref: ${{ env.PR_BRANCH }}
+          ref: "refs/pull/${{ env.PR_NUMBER }}/merge"
 
       - name: Setup Node.js
         uses: actions/setup-node@v4