rdoc 6.13.1 does not detect `private :new`

I'm not sure if this is a bug report or a feature request; I think it has worked in the past but I'm not sure.

Given an input foo.rb:

# Example Foo class should not document private new
class Foo
  class << self
    private :new
  end

  # This should not be documented
  def initialize(...)
  end
end

The generated documentation should not document the new class method.

I can work around this by adding # :nodoc:, but it feels like something that should be detected by the parser.

I'm updating a gem to be Ruby 3.2+, so if there's a better way to mark a private new in those versions that rdoc does detect, I can use that instead.

Start with the foo.rb reproducer and run rdoc to inspect how private :new is represented in the generated documentation. Trace the parser handling of the private declaration and verify that the generated documentation no longer lists the new class method, while initialize remains undocumented.