fix(ci): ensure PR_AUTHOR is present for large_pr_split workflow

Author: heitorlessa

.github/scripts/comment_on_large_pr.js

@@ -1,5 +1,6 @@
 const {
   PR_NUMBER,
+  PR_AUTHOR,
   IGNORE_AUTHORS,
 } = require("./constants")
 

.github/workflows/on_label_added.yml

@@ -18,6 +18,7 @@ jobs:
         uses: actions/github-script@v6
         env:
           PR_NUMBER: ${{ github.event.pull_request.number }}
+          PR_AUTHOR: ${{ github.event.pull_request.user.login }}
         with:
           github-token: ${{ secrets.GITHUB_TOKEN }}
           script: |