Introduce automation to keep `pnpm/action-setup` up-to-date

Hello! This issue was created semi-automatically because this repo popped up in a search. Per https://infra.apache.org/github-actions-policy.html, 3rd-party actions such as `pnpm/action-setup` must be referred to by hash and kept up-to-date by automation such as dependabot. It looks like this repo does not pollow this policy yet.

We plan to start enforcing this policy for `pnpm/action-setup` through https://github.com/apache/infrastructure-actions/pull/1193 .

If this was a false posivite, you can close this issue. Otherwise, you likely want to update your workflows, since they will stop working once that PR is merged.

Start by searching the repository's workflow files for references to pnpm/action-setup and compare them with the Apache GitHub Actions policy. Update the workflows to use a hash-pinned action and add automation such as Dependabot to keep it current. Done means the repository complies with the policy and future updates are automated.

Written by the indexing model from the issue text.