Suppress new Style/RedundantHeredocDelimiterQuotes cop's offenses

Follow up rubocop/rubocop#11528.

This commit suppresses the following new `Style/RedundantHeredocDelimiterQuotes` cop's offenses:

```console
% bundle exec rake
(snip)

Offenses:

test/rubocop/cop/minitest/assert_with_expected_argument_test.rb:82:24: C: [Correctable] Style/RedundantHeredocDelimiterQuotes: Remove the redundant heredoc delimiter quotes, use <<~RUBY instead.
    assert_no_offenses(<<~'RUBY')
                       ^^^^^^^^^

121 files inspected, 1 offense detected, 1 offense autocorrectable
RuboCop failed!
```

test/rubocop/cop/minitest/assert_with_expected_argument_test.rb

@@ -79,7 +79,7 @@ def test_do_something
   end
 
   def test_does_not_register_offense_when_using_assert_equal_with_two_arguments
-    assert_no_offenses(<<~'RUBY')
+    assert_no_offenses(<<~RUBY)
       class FooTest < Minitest::Test
         def test_do_something
           assert_equal(3, actual)