[ruby/drb] Use omit instead of skip for test-unit

https://github.com/ruby/drb/commit/0da149e7a9

test/drb/drbtest.rb

@@ -214,9 +214,9 @@ module DRbCore
   end
 
   def test_06_timeout
-    skip if RUBY_PLATFORM.include?("armv7l-linux")
-    skip if RUBY_PLATFORM.include?("sparc-solaris2.10")
-    skip if defined?(RubyVM::JIT) && RubyVM::JIT.enabled? # expecting a certain delay is difficult for --jit-wait CI
+    omit if RUBY_PLATFORM.include?("armv7l-linux")
+    omit if RUBY_PLATFORM.include?("sparc-solaris2.10")
+    omit if defined?(RubyVM::JIT) && RubyVM::JIT.enabled? # expecting a certain delay is difficult for --jit-wait CI
     Timeout.timeout(60) do
       ten = Onecky.new(10)
       assert_raise(Timeout::Error) do