Pinned "New contributor" GitHub action to v1.

Later versions misidentify all contributors as new ones if the project
does not enable issues.

Follow-up to b7507bad77.

.github/workflows/new_contributor_pr.yml

@@ -12,7 +12,8 @@ jobs:
     name: Hello new contributor
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/first-interaction@v3
+      # Pin to v1: https://github.com/actions/first-interaction/issues/369
+      - uses: actions/first-interaction@v1
         with:
           repo_token: ${{ secrets.GITHUB_TOKEN }}
           issue_message: |