Add support for Ruby 4.0

src/about_iteration.rb

@@ -14,7 +14,7 @@ def as_name(name)
     end
   end
 
-  in_ruby_version("1.9", "2", "3") do
+  in_ruby_version("1.9", "2", "3", "4") do
     def as_name(name)
       name.to_sym
     end

src/about_strings.rb

@@ -159,7 +159,7 @@ def test_in_older_ruby_single_characters_are_represented_by_integers
     end
   end
 
-  in_ruby_version("1.9", "2", "3") do
+  in_ruby_version("1.9", "2", "3", "4") do
     def test_in_modern_ruby_single_characters_are_represented_by_strings
       assert_equal __('a'), ?a
       assert_equal __(false), ?a == 97

src/neo.rb

@@ -70,7 +70,7 @@ def ____(method=nil)
     end
   end
 
-  in_ruby_version("1.9", "2", "3") do
+  in_ruby_version("1.9", "2", "3", "4") do
     public :method_missing
   end
 end

src/path_to_enlightenment.rb

@@ -12,7 +12,7 @@
 require 'about_nil'
 require 'about_hashes'
 require 'about_methods'
-in_ruby_version("2", "3") do
+in_ruby_version("2", "3", "4") do
   require 'about_keyword_arguments'
 end
 require 'about_constants'
@@ -38,7 +38,7 @@
 in_ruby_version("jruby") do
   require 'about_java_interop'
 end
-in_ruby_version("2.7", "3") do
+in_ruby_version("2.7", "3", "4") do
   require 'about_pattern_matching'
 end
 require 'about_extra_credit'