build" use correct json object

.github/workflows/ci.yml

@@ -40,8 +40,8 @@ jobs:
           packages: scheme-basic
       - name: Get PR number
         run: |
-          echo "${{ toJSON(github.event.pull_request) }}" >> pr.json
-          echo "pr_number=$(jq -r '.number' pr.json)" >> $GITHUB_ENV
+          echo ${{ toJSON(steps.release.outputs.pr) }} >> pr_json
+          echo "pr_number=$(jq -r '.number' pr_json)" >> $GITHUB_ENV
         if: ${{ steps.release.outputs.prs_created }}
       - name: Checkout PR code
         uses: actions/checkout@v4