Prevent breaking change for assertion message in test

[koic]

Follow up rubocop/rubocop#11729.

This PR prevents breaking change for assertion message in test. e.g.

% bundle exec ruby -Itest test/rubocop/cop/minitest/lifecycle_hooks_order_test.rb
(snip)

Fabulous run in 0.075080s, 93.2339 runs/s, 93.2339 assertions/s.

  1) Failure:
LifecycleHooksOrderTest#test_registers_offense_when_hooks_are_not_before_test_cases [test/rubocop/cop/minitest/lifecycle_hooks_order_test.rb:62]:
--- expected
+++ actual
@@ -4,7 +4,7 @@
   end

   def setup; end
-  ^^^^^^^^^^^^^^ `setup` is supposed to appear before `test_something`.
+  ^^^^^^^^^^^^^^ Minitest/LifecycleHooksOrder: `setup` is supposed to appear before `test_something`.
   def teardown; end
 end
 "

---

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.