build: fix find-inactive-collaborators workflow token

Use a token that will result in GitHub CI running on the pull requests
that this workflow opens.

Author: Trott

.github/workflows/find-inactive-collaborators.yml

@@ -32,7 +32,7 @@ jobs:
       - name: Open pull request
         uses: gr2m/create-or-update-pull-request-action@v1
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GH_USER_TOKEN }}
         with:
           author: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
           body: This PR was generated by tools/find-inactive-collaborators.yml.