Add CI, merge lcg/ruby-3.0 changes, and fix Ruby 3.2 issues

This pulls in the changes from https://github.com/chef/ruby-shadow/tree/lcg/ruby-3.0, which is the version used by Chef.

This also pulls in:

• https://github.com/apalmblad/ruby-shadow/pull/29
• https://github.com/apalmblad/ruby-shadow/pull/31