build(deps-dev): Update rdoc requirement from ~> 7.1 to ~> 8.0

Updates the requirements on [rdoc](https://github.com/ruby/rdoc) to permit the latest version.
- [Release notes](https://github.com/ruby/rdoc/releases)
- [Changelog](https://github.com/ruby/rdoc/blob/master/History.rdoc)
- [Commits](ruby/rdoc@v7.1.0...v8.0.0)

---
updated-dependencies:
- dependency-name: rdoc
  dependency-version: 8.0.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Gemfile

@@ -21,7 +21,7 @@ group(:generate_references) do
   gem 'pandoc-ruby'
   gem 'pragmatic_segmenter', '~> 0.3'
   gem 'punkt-segmenter', '~> 0.9'
-  gem 'rdoc', '~> 7.1'
+  gem 'rdoc', '~> 8.0'
   gem 'rgen', '~> 0.8'
   gem 'yard', '~> 0.9'
 end