Pathname#mkpath and Pathname#rmtree returns self from Ruby 3.4

Author: hsbt

test/stdlib/Pathname_test.rb

@@ -461,7 +461,7 @@ def test_mkpath
     Dir.mktmpdir do |dir|
       dir = Pathname(dir)
 
-      assert_send_type '() -> nil',
+      assert_send_type '() -> Pathname',
                        dir + 'a/b/c', :mkpath
     end
   end
@@ -642,7 +642,7 @@ def test_rmtree
     Dir.mktmpdir do |dir|
       target = Pathname(dir).join('target')
       target.mkdir
-      assert_send_type '() -> void',
+      assert_send_type '() -> Pathname',
                        target, :rmtree
     end
   end