Fix an error for Style/Documentation

This PR fixes the following error for `Style/Documentation` when using a cbase class.

```ruby
% cat example.rb
class ::MyClass
  def method
  end
end
```

```console
% bundle exec rubocop --only Style/Documentation -d
(snip)

An error occurred while Style/Documentation cop was inspecting
/Users/koic/src/github.com/koic/rubocop-issues/bar/example.rb:1:0.
undefined method `namespace' for s(:cbase):RuboCop::AST::Node
/Users/koic/src/github.com/rubocop/rubocop/lib/rubocop/cop/style/documentation.rb:181:in `qualify_const'
```

changelog/fix_error_for_style_documentation

@@ -0,0 +1 @@
+* [#10234](https://github.com/rubocop/rubocop/pull/10234): Fix an error for `Style/Documentation` when using a cbase class. ([@koic][])

lib/rubocop/cop/style/documentation.rb

@@ -176,7 +176,7 @@ def identifier(node)
         end
 
         def qualify_const(node)
-          return if node.nil?
+          return if node.nil? || node.cbase_type?
 
           [qualify_const(node.namespace), node.short_name].compact
         end

spec/rubocop/cop/style/documentation_spec.rb

@@ -17,6 +17,16 @@ def method
     RUBY
   end
 
+  it 'registers an offense for non-empty cbase class' do
+    expect_offense(<<~RUBY)
+      class ::MyClass
+      ^^^^^^^^^^^^^^^ Missing top-level documentation comment for `class MyClass`.
+        def method
+        end
+      end
+    RUBY
+  end
+
   it 'does not consider comment followed by empty line to be class documentation' do
     expect_offense(<<~RUBY)
       # Copyright 2014