Fixed [error] Cannot pass a value of type (:ref | :raw | nil) as an argument of type (:ref | nil)

```
lib/ruby_header_parser/parser.rb:223:57: [error] Cannot pass a value of type `(:ref | :raw | nil)` as an argument of type `(:ref | nil)`
│   (:ref | :raw | nil) <: (:ref | nil)
│     :raw <: (:ref | nil)
│       :raw <: :ref
│
│ Diagnostic ID: Ruby::ArgumentTypeMismatch
│
└       TyperefDefinition.new(type: typeref_type, pointer: typeref_pointer)
                                                           ~~~~~~~~~~~~~~~

```

Author: sue445

lib/ruby_header_parser/typeref_definition.rb

@@ -8,11 +8,11 @@ class TyperefDefinition
     attr_accessor :type
 
     # @!attribute pointer
-    #   @return [Symbol,nil]
+    #   @return [Symbol,nil] :ref, :raw
     attr_accessor :pointer
 
     # @param type [String]
-    # @param pointer [Symbol,nil] :ref
+    # @param pointer [Symbol,nil] :ref, :raw
     def initialize(type:, pointer: nil)
       @type = type
       @pointer = pointer

sig/ruby_header_parser/typeref_definition.rbs

@@ -1,9 +1,9 @@
 module RubyHeaderParser
   class TyperefDefinition
     attr_accessor type: String
-    attr_accessor pointer: :ref | nil
+    attr_accessor pointer: :ref | :raw | nil
 
-    def initialize: (type: String, pointer: (:ref)?) -> void
+    def initialize: (type: String, pointer: (:ref | :raw)?) -> void
 
     def ==: (untyped other) -> bool