This PR fixes the following build error in the Ruby 3.5 build matrix:

$ bundle exec rake spec
(snip)

==> Failures

  1) RuboCop Project requiring all of `lib` with verbose warnings enabled emits no warnings
     Failure/Error: expect(warnings).to eq []

       expected: []
            got: ["/home/runner/work/rubocop/rubocop/lib/rubocop/cop/style/parallel_assignment.rb:3:
                  warning: tsort wa...om the standard library, but will no longer be part of
                  the default gems starting from Ruby 3.6.0\n"]

https://github.com/rubocop/rubocop/actions/runs/16236943172/job/45848342320

Please see for more details:

• https://bugs.ruby-lang.org/issues/21442
• [Feature #21442] Warn to use tsort gem in the future ruby/ruby#13841

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.