CI: Stub Update with PAT

Created a scoped personal access token to use checkout and push.

This should help with the sporadic 403 errors, likely from timeouts
of the checkout permissions:
  stefanzweifel/git-auto-commit-action#305

.github/workflows/stubs.yml

@@ -30,6 +30,7 @@ jobs:
       with:
         repository: ${{ github.event.pull_request.head.repo.full_name }}
         ref: ${{ github.head_ref }}
+        token: ${{ secrets.PYAMREX_PUSH_TOKEN }}
 
     - name: Pull Remote Changes
       run: git pull