Use omit instead of skip

Author: mrkn

test/ractor_test.rb

@@ -3,7 +3,7 @@
 class NArrayRactorTest < NArrayTestBase
   def setup
     super
-    skip unless defined? Ractor
+    omit "Require Ractor" unless defined? Ractor
   end
 
   data(:dtype, TYPES, keep: true)