* Revert setuptools-rust pin
This was a temporary workaround to fix
https://github.com/certbot/certbot/issues/9111, but it looks like the
the issue resolved itself
* Make mypy happy
There was an unused ignore statement, and Validator.certificate was
unnecessarily casting strings as bytes for an X509 digest method.
* Pin setuptools-rust to prevent build-dep hiccups in the future
