[6.0.x] Added required "issue_message" input to "New contributor" GitHub action.

Backport of dfb04d9472 from main.

.github/workflows/new_contributor_pr.yml

@@ -15,6 +15,10 @@ jobs:
       - uses: actions/first-interaction@v3
         with:
           repo_token: ${{ secrets.GITHUB_TOKEN }}
+          issue_message: |
+            Hello! Thank you for your interest in Django 💪
+
+            Django issues are tracked in [Trac](https://code.djangoproject.com/) and not in this repo.
           pr_message: |
             Hello! Thank you for your contribution 💪