[BUG] Replace repo_token with github_token in Auto Assign PR GHA (#…

…17203)

The Auto Assign GHA workflow fails with this [error](https://github.com/rapidsai/cudf/actions/runs/11580081781). This PR fixes this error.
xref #16969

Authors:
  - Matthew Murray (https://github.com/Matt711)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: #17203

.github/workflows/auto-assign.yml

@@ -13,5 +13,5 @@ jobs:
     steps:
       - uses: actions-ecosystem/action-add-assignees@v1
         with:
-          repo_token: "${{ secrets.GITHUB_TOKEN }}"
+          github_token: "${{ secrets.GITHUB_TOKEN }}"
           assignees: ${{ github.actor }}