Use secrets to allow PR commenting

[djmitche]

From the last link, this article describes a way to use secrets. It is a bit verbose and requires creation of a separate workflow but doable. I will try to implement it this week.

Oh nice! I think this could also be used to comment on Comprehensive Rust PRs with timing information like @djmitche tried to do recently: https://github.com/google/comprehensive-rust/pull/1576.

Originally posted by @mgeisler in https://github.com/google/mdbook-i18n-helpers/issues/148#issuecomment-1906015582

[djmitche]

Notably, this didn't actually require secrets.