Add test to ensure unsafe cops are properly configured

[ydah]

Follow up: https://github.com/rubocop/rubocop/commit/7cda5aedc5ccf24ce53bccdb258a9e4dbac3ec16

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Before submitting the PR make sure the following are checked:

• [x] Feature branch is up-to-date with master (if not - rebase it).
• [x] Squashed related commits together.
• [x] Added tests.
• [-] Updated documentation.
• [-] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• [x] The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

[bquorning]

I noticed that our specs are flaky, and git-bisect tells me it happened after this PR.

Here’s a minimal failing spec run:

bundle exec rspec './spec/project/default_config_spec.rb[1:8]' './spec/rubocop/rspec/description_extractor_spec.rb[1:1]' --seed=28987

[ydah]

@bquorning Thank you. I fixed it: https://github.com/rubocop/rubocop-rspec/pull/1855