Pin actions/labeler to v4 [skip ci] (#4038)

RAPIDS repos are using the `main` branch of https://github.com/actions/labeler which recently introduced [breaking changes](https://github.com/actions/labeler/releases/tag/v5.0.0).

This PR pins to the latest v4 release of the labeler action until we can evaluate the changes required for v5.

This PR also moves the labeler workflow to the correct location in the repo.

Authors:
   - Ray Douglass (https://github.com/raydouglass)

Approvers:
   - AJ Schmidt (https://github.com/ajschmidt8)

github/workflows/labeler.yml → .github/workflows/labeler.yml

@@ -6,6 +6,6 @@ jobs:
   triage:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/labeler@main
+    - uses: actions/labeler@v4
       with:
         repo-token: "${{ secrets.GITHUB_TOKEN }}"