Try to fix CI

Author: luke-gruber

test/ruby/test_transcode.rb

@@ -2390,9 +2390,9 @@ def test_ractor_asciicompat_encoding_doesnt_exist
       rs = []
       NO_EXIST = "I".freeze
       7.times do
-        rs << Ractor.new do
+        rs << Ractor.new(Encoding::Converter) do |conv|
           500.times do
-            if (val = Encoding::Converter.asciicompat_encoding(NO_EXIST)) != nil
+            if (val = conv.asciicompat_encoding(NO_EXIST)) != nil
               raise "Got #{val}, expected nil"
             end
           end