workflows/new-issues: Use an llvmbot token to add labels (#120840)

There is a separate job that mentions teams based on the label added,
and this job won't run if we use the default github token.

Author: tstellar

.github/workflows/new-issues.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
       - uses: llvm/actions/issue-labeler@main
         with:
-          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          repo-token: ${{ secrets.ISSUE_SUBSCRIBER_TOKEN }}
           configuration-path: .github/new-issues-labeler.yml
           include-title: 1
           include-body: 0