Remove dependency on ostruct

Requiring ostruct on Ruby 3.4 warns:
```
/home/user/.rbenv/versions/3.4.1/lib/ruby/gems/3.4.0/gems/gem-release-2.2.2/lib/gem/release/data.rb:2: warning: /home/user/.rbenv/versions/3.4.1/lib/ruby/3.4.0/ostruct.rb was loaded from the standard library, but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
Also please contact the author of gem-release-2.2.2 to request adding ostruct into its gemspec.
```

But since the values that this ostruct will take is known, there is no need to use ostruct all all. I've simply replaced it with a normal struct.
It's a bit akward because of support for such old ruby versions (no `keyword_init`) but works out.

lib/gem/release/data.rb

@@ -1,26 +1,18 @@
 require 'erb'
-require 'ostruct'
 require_relative 'helper/string'
 
 module Gem
   module Release
     class Data < Struct.new(:git, :gem, :opts)
       include Helper::String
 
+      KEYS = %i[
+        gem_name gem_path module_names author email homepage
+        licenses summary description files bin_files
+      ].freeze
+
       def data
-        {
-          gem_name:     gem_name,
-          gem_path:     gem_path,
-          module_names: module_names,
-          author:       user_name,
-          email:        user_email,
-          homepage:     homepage,
-          licenses:     licenses,
-          summary:      '[summary]',
-          description:  '[description]',
-          files:        files,
-          bin_files:    bin_files
-        }
+        KEYS.map { |key| [key, send(key)] }.to_h
       end
 
       private
@@ -41,11 +33,11 @@ def user_login
           git.user_login || '[your login]'
         end
 
-        def user_name
+        def author
           git.user_name || '[your name]'
         end
 
-        def user_email
+        def email
           git.user_email || '[your email]'
         end
 
@@ -72,6 +64,14 @@ def bin_files
         def strategy
           STRATEGIES[(opts[:strategy] || :glob).to_sym] || STRATEGIES[:glob]
         end
+
+        def summary
+          '[summary]'
+        end
+
+        def description
+          '[description]'
+        end
     end
   end
 end

lib/gem/release/files/template.rb

@@ -59,7 +59,7 @@ def binding
           end
 
           def context
-            Context.new(data)
+            Context.new(*data.values)
           end
       end
     end

lib/gem/release/files/template/context.rb

@@ -2,7 +2,7 @@ module Gem
   module Release
     module Files
       class Template
-        class Context < OpenStruct
+        class Context < Struct.new(*Gem::Release::Data::KEYS)
           class Const < Struct.new(:type, :names)
             def define(&block)
               lines = build(names) { |name| "#{type} #{name}" }