Update test helpers for YAMLSerializer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hsbt

test/rubygems/helper.rb

@@ -738,11 +738,7 @@ def write_dummy_extconf(gem_name)
   # Load a YAML string, the psych 3 way
 
   def load_yaml(yaml)
-    if Psych.respond_to?(:unsafe_load)
-      Psych.unsafe_load(yaml)
-    else
-      Psych.load(yaml)
-    end
+    Gem::SafeYAML.safe_load(yaml)
   end
 
   ##

test/rubygems/test_gem_commands_owner_command.rb

@@ -55,8 +55,6 @@ def test_show_owners
   end
 
   def test_show_owners_dont_load_objects
-    pend "testing a psych-only API" unless defined?(::Psych::DisallowedClass)
-
     response = <<EOF
 ---
 - email: !ruby/object:Object {}
@@ -70,7 +68,7 @@ def test_show_owners_dont_load_objects
 
     @stub_fetcher.data["#{Gem.host}/api/v1/gems/freewill/owners.yaml"] = HTTPResponseFactory.create(body: response, code: 200, msg: "OK")
 
-    assert_raise Psych::DisallowedClass do
+    assert_raise ArgumentError do
       use_ui @ui do
         @cmd.show_owners("freewill")
       end

test/rubygems/test_gem_package.rb

@@ -909,7 +909,11 @@ def test_verify_checksum_bad
       }
       tar.add_file "checksums.yaml.gz", 0o444 do |io|
         Zlib::GzipWriter.wrap io do |gz_io|
-          gz_io.write Psych.dump bogus_checksums
+          if Gem.use_psych?
+            gz_io.write Psych.dump(bogus_checksums)
+          else
+            gz_io.write Gem::YAMLSerializer.dump(bogus_checksums)
+          end
         end
       end
     end
@@ -955,7 +959,11 @@ def test_verify_checksum_missing
 
       tar.add_file "checksums.yaml.gz", 0o444 do |io|
         Zlib::GzipWriter.wrap io do |gz_io|
-          gz_io.write Psych.dump checksums
+          if Gem.use_psych?
+            gz_io.write Psych.dump(checksums)
+          else
+            gz_io.write Gem::YAMLSerializer.dump(checksums)
+          end
         end
       end