Also update the reviewer list.

ci: remove "needs:response" label if author responds

The default behavior of the stale action is to indiscriminately remove
the `needs:response` label for any activity whatsoever, from anyone. The
other option is to turn it off completely, meaning the maintainers needs
to manually remove the label themselves when the author responds for an
issue to not close automatically. Neither of these behaviors are useful
to us.

Using team reviewers when possible reduces the churn on the git history
as we'll be able to add or remove reviewers without needing to change
the workflow files.

This requires using Github fine-grained personal access tokens with Pull
Requests set to "Read and write" and Members to "Read-only".