Require Ruby >= 3.3 and update CI Ruby versions

[dduugg]

Summary

Ruby 3.2 is now EOL. This PR raises the minimum supported Ruby to 3.3 and refreshes CI so the test matrices target the supported set (3.3 and 3.4, plus the repo's intentional 4.0 entry).

Motivation: resolve Ruby version restrictions from rubyatscale/pack_stats#56, where supporting EOL Ruby forced older/vulnerable transitive dependencies.

Changes

• code_ownership.gemspec: required_ruby_version raised from Gem::Requirement.new('>= 3.2', '< 4.1.dev') to Gem::Requirement.new('>= 3.3', '< 4.1.dev') (upper bound preserved).
• .github/workflows/ci.yml: stable-ruby-versions matrix now ['3.3', '3.4', '4.0'] (dropped 3.2).
• .github/workflows/cd.yml: stable-ruby-versions matrix now ['3.3', '3.4', '4.0'] (dropped 3.2); the ruby-version: '4.0' build pin is unchanged.
• .rubocop.yml: TargetRubyVersion raised from 3.2 to 3.3.

Notes

• .ruby-version (4.0.1) is already >= 3.3 and was left unchanged.
• The intentional '4.0' matrix entries were preserved.
• No bundle install was run and Gemfile.lock is unchanged.
• Latest stable Ruby is 3.4.9; 3.5 is preview-only and not included.