Cannot use `@!scope class` on an attribute defined by `attr_*`

[UlyssesZh]

If I add @!scope class for a attr_* call (such as attr_reader :test), there is an error.

Discussion context: #1581.

Steps to reproduce

Write these to lib/test.rb:

# A test class.
class Test

  # @!scope class
  # A test attribute.
  attr_reader :test
end

Then run yard doc --debug.

Actual Output

[debug]: Parsing ["{lib,app}/**/*.rb", "ext/**/*.{c,cc,cxx,cpp,rb}"] with `ruby` parser
[debug]: Parsing lib/test.rb                                                                   
[debug]: Serializing to .yardoc/objects/root.dat
[debug]: Re-generating object ...                                                                                                                                                             
[debug]: Re-generating object Test...                                                                                                                                                         
[debug]: Generating asset js/jquery.js                                                                                                                                                        
[debug]: Serializing to doc/js/jquery.js                                                                                                                                                      
[debug]: Generating asset js/app.js                                                                                                                                                           
[debug]: Serializing to doc/js/app.js                                                                                                                                                         
[debug]: Generating asset js/full_list.js
[debug]: Serializing to doc/js/full_list.js
[debug]: Generating asset css/style.css
[debug]: Serializing to doc/css/style.css
[debug]: Generating asset css/common.css
[debug]: Serializing to doc/css/common.css
[debug]: Generating asset css/full_list.css
[debug]: Serializing to doc/css/full_list.css
[debug]: Generating asset class_list.html
[debug]: Serializing to doc/class_list.html
[debug]: Generating asset method_list.html
[debug]: Serializing to doc/method_list.html
[debug]: Generating asset file_list.html
[debug]: Serializing to doc/file_list.html
[debug]: Generating asset frames.html
[debug]: Serializing to doc/frames.html
[debug]: Serializing to doc/index.html
[debug]: Serializing to doc/_index.html
[debug]: Serializing to doc/top-level-namespace.html
[error]: Exception occurred while generating 'Test.html'
[error]: NoMethodError: undefined method `[]' for nil
[error]: Stack trace:
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/html/attribute_details.erb:8:in `block (2 levels) in _erb_cache_24'
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/html/attribute_details.erb:6:in `each'
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/html/attribute_details.erb:6:in `each_with_index'
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/html/attribute_details.erb:6:in `block in _erb_cache_24'
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/setup.rb:155:in `block in scopes'
        /home/ulysses/.local/share/gem/ruby/3.3.0/gems/yard-0.9.37/templates/default/module/setup.rb:153:in `each'

Files:           1
Modules:         0 (    0 undocumented)
Classes:         1 (    0 undocumented)
Constants:       0 (    0 undocumented)
Attributes:      0 (    0 undocumented)
Methods:         1 (    0 undocumented)
 100.00% documented

Expected Output

Should be equivalent to what this would do:

# A test class.
class Test

  # @!scope class
  # @!attribute [r] test
  # A test attribute.
end

Environment details:

• OS: NixOS 24.05
• Ruby version (ruby -v): 3.3.4
• YARD version (yard -v): 0.9.37

I have read the Contributing Guide.