Fix octokit.rest.issues.addLabels call (#76601)

Follow-up for #76544.

[Failed worflow
run](https://github.com/vercel/next.js/actions/runs/13560755436/job/37903278074)

The PR number was incorrectly retrieved from the
`octokit.rest.pulls.create` response.

Author: unstubbable

scripts/automated-update-workflow.js

@@ -69,7 +69,7 @@ async function main() {
   await octokit.rest.issues.addLabels({
     owner,
     repo,
-    issue_number: pullRequest.number,
+    issue_number: pullRequest.data.number,
     labels: ['run-react-18-tests'],
   })