Incorporate unmerged PRs from upstream

[tpowell-progress]

Description

Incorporate the following PRs:

• extconf.rb: use Rbconfig::CONFIG instead of mkmf CONFIG apalmblad/ruby-shadow#31 (breakage starting in Ruby 3.2)
• Removes taint checking functions apalmblad/ruby-shadow#29 (taint functions removed in Ruby 3.2: https://bugs.ruby-lang.org/issues/16131)

Bumped the version to 3.0.0 and changed the gem name to chef-ruby-shadow (this fork already existed) as the above PRs are approaching 3 years old.

Related Issue

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (non-breaking change that does not add functionality or fix an issue)

Checklist:

• I have read the CONTRIBUTING document.
• I have run the pre-merge tests locally and they pass.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• If Gemfile.lock has changed, I have used --conservative to do it and included the full output in the Description above.
• All new and existing tests passed.
• All commits have been signed-off for the Developer Certificate of Origin.